Ant Identification, Biology and Control

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Category: 7A

Ant Morphology

Morphology is the study of structure. Ant morphology (parts) is used in species identification. The following is a brief review of ant morphology. As with all insects, ants have 3 major body parts, namely the head, thorax, and gastor (abdomen). The thorax can be divided into 2 major parts, the alitrunk which contains the legs and wings, and the petiole which connects the alitrunk to the gastor. The petiole is a waist or stalk that dorsally bears 1 or 2 bump-like structures or nodes. Ants have mandibles (jaws) which vary in structure. These structures provide a multitude of functions, ranging from grasping, tearing, cutting and other special tasks. Most ants have a stinger at the end of the abdomen. The stinger is only found in females, because it is a modified ovipositor (egg laying organ). Ants have compound eyes which are the major organs that form images. Vision in most ants is poor when compared to that of vertebrates. Some ants have simple eyes (ocelli) that function to perceive light intensity. They appear as small raised circles or humps that are found between the compound eyes. On the other hand, the antennae are the major organs used to perceive their environment and therefore regulate their behavior. The antennae function as olfactory organs (smell) and perceive temperature, vibration and humidity. Ants have elbowed antennae. With elbowed antennae, the pedicel (second and longest segment) is characteristically elongated and frequently as long as the remaining segments (flagellum).

Most of these insects possess a gland found on the petiole called the metapleural gland. Secretions of this organ contain antibacterial and antifungal chemicals that aid in survival in the dark, humid nests that are typically found in the ground or rotting vegetation. In addition, this organ produces an antiseptic that acts as a repellent to attacking organisms and is thought to release pheromones for communication. The basic morphology of an ant is illustrated below.

File:Scheme ant worker anatomy-en.svg
Ant Diagram.: Image courtesy of Mariana Ruiz (User:LadyofHats), Wikimedia Commons

Ant Success

Ants are the first and only social insect-predators that frequently rely on rotting vegetation and moist, dark, soil as a nesting site. The reproductive forms of these insects shed their wings subsequent to mating and then crawl into smaller spaces than wasps. The wings and a relatively large thorax of wasps limit where they can nest. The ants obviously have the same defensive weapons of the wasp, namely the stinger and other chemical weapons. 

One of the greatest advantages for ants is their social behavior. Working as a colony with individuals performing specialized duties, they are more efficient than non-social insects in accomplishing needed activities. For example, when there are a number of individuals solely responsible for feeding larvae or young, there is a higher likelihood that the larvae will be fed by at least 1individual. With social insects, there is a division of labor. Some ants in the colony are responsible for bringing food to the feeders. Others are responsible for protecting the colony. The feeders are specialized to complete their single task, and  do not have to succeed at a great number of tasks to get the food to the larvae.

The metapleural gland excretes antifungal and antibacterial materials that ants spread throughout their colonies. This protects their brood and their food supplies in the humid underground environment. Ants are among the most highly evolved of insects. The variety of lifestyles displayed by these insects is amazing, perhaps because so many of their social behaviors seemingly parallel our own.

Mutualism. Ants and other Animals

Ants have developed mutualistic relationships with other ants, insects, animals and plants. Mutualism occurs when 2 organisms are in close associations with each other with both benefiting.

Aphids and Ants. Aphids secrete large amounts of honeydew. They feed on plant sap that is high in sugars but low in nitrogen. Since they need more nitrogen than provided by normal feeding, they suck excessively and excrete the excess sugars through the anus as a clear, sticky, partially digested sap, or honeydew. Some aphids excrete their own body weight in honey.dew every hour.

Honeydew producing insects normally have a mutualistic relationship with ants. Ants are drawn to aphids and frequently tend or 'milk' them for the honeydew. They frequently will approach an aphid from behind and first stroke one side of the abdomen with their antennae and then the other side. Soon a drop of honeydew is expelled and subsequently consumed by the ant. The ant's benefit is obvious because the honeydew is food. Aphids also benefit from the presence of the ants. Aphids are vulnerable to a large number of predators and parasitoids. The activity of the ants keeps the aphid-eating insects away. In many cases, the ants, being active predators themselves, will eat other predators instead. They rarely eat the aphids.

Some ant species carry this mutualistic relationship to extremes. They may herd, push, or carry the aphids to the terminal ends of the plants where growth is new and more nutritious plant sap occurs, thus resulting in an increase in the quantity and quality of honeydew. There are even a few species that will carry their “pets” from plant to plant in search of better feeding locations. These ants will also round up their aphids and places them in groups under large leaves with the threat of rain. Some species will build igloo-like shelters out of bits of debris over individual aphids, leaving enough room at the top to tend the aphids for honeydew but not enough for the aphids to escape. This insures the ant a constant source of food and protects the aphids from predators and parasites. It is well established that ants are the only species of animal besides humans that is known to keep pets.

During the winter months when little or no plant sap is available, there is one species of ant that will collect the eggs of aphids and take them to its nest below ground. In the spring, when plants begin to grow again, the eggs are removed from the nests and placed on the plants which subsequently hatch to produces aphids that soon begin production of honeydew.

Amazingly, the news queens of a few ant species carry honeydew producing scale insects in their mandibles when they depart from the nest on their nuptial flight. After mating and settling to the ground, they are ready to start a new colony with the start of a food source, namely the honeydew producing scales.

The most complete and remarkable symbiotic relationship between ants and honeydew producing insects was first discovered in 1980. In this case, there is a species of rain forest ant that feeds entirely on honeydew produced by a species of mealybug. The mealybugs are carried to and from the ants’ nest to certain trees and shrubs that are as far away as 60 feet. The ants do little conventional nest-building but locate preformed cavities in dense brush or trees. Much of the perimeter walls of the nests are formed by the ants bodies, much like what occurs with army ants. They cling to one another to create a solid mass that shields their own brood and of course the mealybugs. A fully developed colony contains a single queen, over 10,000 worker ants and about 9,000 mealybugs. The transport of the mealybugs between the 2 sites is intense: at any time as many as 10 % of the worker ants are carrying mealybugs in their mandibles. The location of the ants' nest is by no means permanent. If necessary, ants will readily move a nest to a new location. These ants are true nomadic ranchers, but their stock is meal bugs, not cattle, and the ranchers are ants, not people.

Some aphids that depend on ants for their protections have acquired structural and behavioral adaptations. These typically have smaller or lack cornicles. As a result, they  may lack the defensive chemicals produced by these insects. In addition, they have a thinner protective coat of waxes on the outside of their bodies than do aphids that are  tended by ants. Aphids that are not typically tended by ants forcibly propel honeydew drops well away from their body. This behavior keeps them free from this sticky-gummy liquid and the fungus that develops upon it. On the other hand, tended aphids gently oozes the honeydew from there anus making it readily available to ants. Many have a basket of hairs around the anus to hold the honeydew in place until consumed. If not readily consumed by ants, the honeydew is even withdrawn back into the aphid until a later time.

Ants and Plants. Some ants survive by controlling the environment in which they live. In the Amazon rain forests, there is a tremendous diversity of vegetation. If you walk through the forest, no plant typically dominates, and  you may not see any 2 plants of the same species within hundreds of yards. One notable exception is the cordia tree. On occasion, you will find a large stands of these trees with no other plants in the vicinity. In addition, these stands are typically encircled by large barren strips of land. The reason for this phenomenon is the presence of a small ant species that lives within the stems of these trees. They are very protective of the trees killing any plant feeding insects. They will also swarm on and attack any larger animal venturing into the stand. In addition, any other species of plants that germinates within the stand quickly shrivels and dies due to the ants stinging and injecting venom into the terminal buds. As might be expected, the barren areas surrounding the stand of trees is similarly cleared by the stinging of these ants. Of course, the ants benefit from this symbiotic relationship since they are provided by a safe bountiful location for their nests. And the trees benefit as they are provided with an endless competitively free environment in which to expand their growth. People living in the rain forest refer to the barren areas as the “devil’s garden” and refrain from planting crops there.

Ants and Other Ants. Slave-maker ants commonly steal brood from other species of ant colonies. They subsequently take them back to their colonies and use the captured brood to develop and serve the slave-maker colony. The slaves are absolutely dependent in that if they don't work, they are not fed by their masters. Other ant species work together, such as the Crematogaster limata parabiotica and Monacis debilis; the often construct their nests close together and frequently share the same foraging trails. The former species has also been observed giving food to the Monacis workers.

Ant Wars, Competition, and Survival. Ants are among the most aggressive and war-like of all animals. If ants had a policy of life, it could be summarized as restless aggression, territorial conquest, and total annihilation of neighboring colonies. These insects use any of a number of strategies and weapons to reach these ultimate goals. Chemical warfare is prevalent among many species, including spraying a variety of toxic chemicals in order to repel, confuse, immobilize or even kill their rivals. The soldiers of many species readily assume a kamikaze role in order to “win skirmishes” between rival colonies. One of the most dramatic of these sacrifices is exhibited by a carpenter ant from SE Asia. These ants act as walking bombs. There is a huge internal gland that occupies much of their body that is filled with toxic chemicals. If one of these ants is hard pressed by a rival ant or predator, it contract some large abdominal muscles that violently bursts open the abdomen (like a bomb) releasing the chemicals.

The limited availability of food frequently is important in colony survival. As a consequence, rival colonies frequently develop strategies to maximize their collection of available food. There is a tiny fast moving ant in the deserts of Arizona that utilizes toxic secretions to intimidate and confuse much large honey ants, as they steal food from the larger ant colonies. In addition, these tiny ants will frequently prevent honey ants from leaving their nests by releasing toxic chemical down the hole or nest entrance, thus driving the former below ground. This of course allows the smaller species to forage without competition from the honey ants. Another form of nest entrance blocking is exhibited by a small ant species in the southwestern deserts. In this case, they gather in mass around the nest entrance of their rivals and similarly release toxic chemicals down the entrance. However, they also pick up pebbles, twigs and other small objects and drop them down the vertical shaft entrance. 

Possibly the most elaborate of all documented aggressive strategies in social insects occurs in battles between the tiny woodland ant and the imported fire ant. The fire ants are deadly enemies of the woodland ants with colonies 100 times larger than their tiny rivals. Even though fire ants are much more powerful than the woodland ants, both successfully survive in the same area. The secret of woodland ant survival is primarily based on a specialized soldier (major) and a 3-stage strategy to defend against fire ant attack. These soldiers are equipped with huge heads that are equipped with large sharp jaws provided with massive muscles. These ants do not attempt to sting or spray their enemy with poisons (common in many ants), but they quite precisely use their mandible to snip off legs, heads and other body parts. Unless attacked, the majors remain in the colony. However, the minors regularly forage for food but are always on the alert for scout fire ants that are looking for colonies to raid. If a woodland ant forager encounters a fire ant soldier close to its colony, it violent response is triggered. Once detected, the minor rushes to the fire ant in a mock attack but merely touches the potential invader in order to acquire some of its odor. She then quickly retreats toward her nest. As she retreats, she lays a pheromone trail by periodically touching her abdomen to the ground. On her way back, she briefly rushes up to any other minor alerting them to the presence of the fire ant scout. Once in the nest, soldiers plus many of the minors are alerted to the presence of the invader scout (by its smell on the minor worker). As a result, they subsequently rush in mass along the already establish pheromone trail leading to the enemy. Once found, the soldier surrounds the fire ant and attack relentlessly and are fully capable of destroying it due to their great superiority in numbers. Of course, the whole purpose is to kill the fire ant scout before it can alert other fire ants in the area as to the presence of a woodland ant colony. Once this is accomplished, the soldiers search the general area for any other fire ant scouts.

If fire ants mount a full scale attack of a woodland ant colony, the defenders have an alternate strategy. As fire ants arrive in full force, the entire force of woodland soldier ants is sent into the battle. Soon the battle ground is littered with the bodies of the smaller species plus a multitude of legs and other body parts of the fire ants. As the battle continues, any woodland ant minors still present retreat to the nest. As more and more fire ants arrive and the woodland ant soldiers are greatly out-numbered, they retreat, close ranks to form a dense protective perimeter around their colony entrance. With the impending doom that the fire ants will soon break through the protective barrier and ravage, steal and consume the woodland ant’s eggs, larvae and pupae, the activity of the minors in the colonies is frantic but well programed. They gather the young in their mandibles and sprint out though the colony entrance, through the battle field and beyond to safety. The woodland ant soldiers remain true to their programmed behavior and fight to the death. Once the fire ants leave the now ravaged colony, the minors return with their cargo of eggs, larvae and pupae and reestablish colony life. Over time new soldiers develop in the colony preparing for the possibility of another raid. Such is the life of ants!

Division of Labor. All living ant species have a caste system. The main castes consist of kings, queens, and workers. The kings are winged reproductive males that contribute absolutely nothing to the labor of the colony. The winged females swarm with the males, similarly to the behavior seen in termites. Eventually, they will become the queens of new colonies. During the establishment of a new colony, the new queen initially performs all the work tasks, but once her first brood of worker larvae is reared to adulthood, her sole duty is to lay eggs. Unlike termites, ant colonies may have many queens, in some cases hundreds.

Workers are sterile females and can be both the laborers and defenders of the colony. In most ant species, there can be sub-castes of the workers, namely majors, media and minors. Relative head and overall body size distinguishes sub-castes. The majors are the largest of the 3 and possess a disproportionately large head and mandibles. The function of the soldiers is to protect the ant colonies. The media and minor workers are the most common individuals in an ant colony and perform the majority of the work duties. Minor worker ants also perform a variety of functions depending on the species of ant.

Mating Behavior. Most all ants mate in 1 of 2 ways. The first is known as the male-aggregation syndrome. In this case, males and unfertilized queens are triggered to swarm from their nest. This swarming often appears as a column of flying ants rising off the ground. The queen is usually inseminated in mid-air and then flies off to start a new nest. Once breaking off her wings she digs into the ground or other substrate to form a small cavity, the beginning of a new nest. She lays her eggs and remains with them until they hatch, living off of her own body reserves, including dissolving her wing muscles. Eventually, they will hatch and become the first of her workers that will take care of her and the colony as it increases in size and numbers

The second type of mating technique occurs when queens aggregate at the surface of the colonies and attracts males by releasing sex pheromones. There are a variety of exceptions to this basic type of mating. In some cases, females mate on the ground and subsequently fly off to begin their nests. With other species, the males swarm close to the ground until females emerge from their colonies. Once emerged, they surround her in a rolling, writhing ball until the newly inseminated female escapes and flies away to establish a nest site.

Field Ants (Formica spp).

These are relatively large ants (3/8 inches  in length) and are often confused with carpenter ants. There is a large variation in color ranging from black, brown, tan or red. Their thorax, when viewed from the side, appears uneven or notched. The petiole (waist) bears a single distinct node. A key characteristic is the presence of 3 ocelli or simple eyes on the front of the head between the compound eyes.

This is one of the main species that occurs throughout North America; however, this is a very diverse genus with over 100 North American species. As the name wood ant implies, many Formica species live in wooded areas where there exists no shortage of material with which they can collect for their mounds. However, sunlight is important to most Formica species and colonies rarely survive for any considerable period in deeply shaded, dense areas. The majority of species, especially outside the rufa species group, are inhabitants of more open woodlands or treeless grassland or shrub-lands. In North America, these habitats had a long history of frequent large scale fires that kept them in open areas before European settlement. Conversion to agriculture and fire suppression has reduced the abundance of most American Formica. However, at least a few Formica species may be found in a wide range of habitats from cities to seaside to grasslands to swamps to forests of the temperate Northern Hemisphere

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Formica rufa. Image courtesy of Richard Bartz, Munich Marko Freak, Wikimedia Commons

They typically nest in soil or decayed logs and sometimes are referred to as mound or thatching ants because some species construct their nests out of twigs, grass, stems, leaves, and pine or fir needles. They are rarely found indoors and have not been found to nest indoors but are common around homes and other buildings. Their large mounds may blemish lawns. Field ants will also nest in leaf litter or mulch that is more than 2 inches thick and can live under stones, firewood, or other debris that might be found in a lawn

Image: Field ant nest found in wooded area. Image courtesy of Walter Siegmund CC BY-SA 2.5

Field ants can become aggressive if their nests are disturbed but rarely sting but can readily bite. The bite can penetrate the skin. In addition, they can spray formic acid which will sting if delivered to an open wound.

Big Headed Ants (Phieidole spp.)

Most species of Pheidole are dimorphic. This means that colonies contain 2 castes of workers, namely the minors, workers, and major workers, and soldiers. The latter generally have enormous heads and mandibles in comparison to their usually fairly modest body size. There are estimated to be nearly 1,000 species worldwide. They have a 2 segmented pedicel (waste) and 2 spines on the thorax. The antennae are 12-segmented with a 3-segment terminal club. The majors are easily identified by their enlarged heart shaped head. The minors are frequently confused with fire ants.

They can become aggressive, if the nest is disturbed, but rarely if ever sting but can readily bite. The bite can penetrate the skin. In addition, they can spray formic acid which will sting if delivered to an open wound.

Big-headed ant (Pheidole spp). Image Courtesy Ant Web. org, April Nobile CC BY SA 3.0

There are several species commonly found in Florida and Hawaii. In the western U.S., a few have been collected but are not yet reached a pest status. In the U.S., most species are found in warm dry areas.

As indicated, these ants are similar to fire ants, but may be distinguished from the latter by the presence the 12-segmented antennae terminating in a 3 segmented club and the enlarged head of the majors. The head of these are so large that it appears that they have trouble walking. Colonies are normally found in soil, but occasionally invade structures when foraging. Nests are typically located under rocks, logs, miscellaneous debris or other objects as well as cavities in rotting wood and old termite galleries. Big-headed ants feed on a variety of materials, both protein and carbohydrates. They typically forage short distances in distinct trails. Protein seems to be preferred when foraging in structures.

The major workers of a Pheidole colony, while they may look fierce, are often quite shy and are often the first to flee on any hint of danger. Interestingly, many Pheidole species are the prey of parasitoidal phorid flies that lay their eggs on the major workers; the fly larvae grow mainly in the head capsules of the victims and eventually decapitating them. They probably would starve in the bodies of minor workers.

In most cases, the major workers remain within the nest to break up large food items, or outside to carry large items like seeds; many Pheidole species are ecologically important seed consumers ("harvesters").

Acrobat Ant (Crematogaster sp.)

Most acrobat ants are black to brown, a few are multicolored with the head or abdomen darker than the rest of the body. Most species are 1/16 to 1/8 inches long. The workers are monomorphic, meaning they are similar in size and shape. One clue for identification is that they have a 2-segmented petiole (waist) that attaches to the front part of the abdomen. The thorax bears a pair of spines. The abdomen is hart shape when viewed from above. Their name is based on the characteristic poise they take when alarmed. In this case the abdomen is raise above the thorax and abdomen. It almost looks as if they are standing on their heads.

Image. Acrobat ants with  heart shaped abdomens. Image courtesy of April Noble CC BY-SA 3.0

These ants readily consume honeydew produced by aphids and other Homoptera and live or dead insects. Their nests are typically found under objects such as log, rocks, firewood, and decaying trees.  On occasion, they will strip the insulation from electrical or telephone wires, possibly resulting in short circuits. Inside structures, acrobat ants are attracted to sweets and high-protein foods (meats). They frequently form their nests in wall voids, baseboards, door and window frames. These frequently occur when these structures have been damaged by moisture or previously infested with other insects,  such as wood destroying beetles or termites. When infestations of acrobat ants are found in structures, they typically gain access along fences, decks, electrical and telephone lines and tree limbs in contact with the structure. In addition, these ants also can gain access to homes through many small entry points around doors, windows, and vents. 

If an acrobat nest is disturbed, they are aggressive and produce a distinct defensive odor. Nests of this species are large and frequently number in the thousands. Indoor invasion typically comes from outdoor nests located in tree stumps or logs. An unusual habit is their nesting in foam core panel insulation.

Argentine Ant (Linepithema humile)

The Argentine ant has a single node and is a small, shiny brown ant with only 1 size of worker.. The queen ants are much larger than workers, sometimes reaching 1/4 inch in length.

The Argentine ant is worldwide in distribution. It is well established throughout the Southeast, California and Hawaii. It has also been reported in Arizona, Missouri, Illinois, Maryland, Oregon, and Washington.

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Image: Argentine ant tending a scale for honeydew. Image courtesy of Penarc  CC  BY-SA 4.0

Argentine ants nest outdoors under logs, concrete slabs, debris and mulch. They ants build very large colonies, which they frequently relocate. During winter months, this ant will move indoors.

This ant is successful and hard to control because:

  1. Different Argentine ant colonies in a same general locale are not enemies. Even the many queens in a single colony or separate colonies are friendly to each other.

  2. Argentine ants are not too "picky" when choosing a suitable site to infest or colonize. They readily move their nests during the changing seasons and other conditions.

  3. These pests are omnivorous; they seem to never be in short supply of food.

  4. Each colony of Argentine ants contains a multitude of workers.

  5. Each worker is more courageous and harder worker than most ants. Creatures that attempt to prey on Argentine ants are confronted with an army of stubborn workers that never runs from a fight!

  6. The queens of most ant species are usually egg-laying machines. The queen ants actually helps in the care, grooming and feeding of the young.

  7. Most species of ants mate and reproduce by swarming.

  8. A swarmer reproductive (as seen with fire ants and carpenter ants) has about 1 chance in 1,000 of surviving and successfully reproducing. The Argentine ant queen always succeeds!

It was discovered a few years ago that colonies of these ants in Argentina were territorial and aggressive toward each other and would actually tear one another apart when coming in close contact. A question arose as to why didn’t these ants act the same way in California? Why would ants from San Diego that were dropped into a colony in San Francisco not be aggressive toward each other, while in Argentina colonies a few hundred meters very aggressive to each other. One answer was that they have super-colonies. In California, it is thought that one of these colonies stretch for 560 miles along the coast. 

Researcher compared the genetic differences among the ants in Argentina to those in different areas of California, namely from San Diego to Ukiah. As a result, it was found that the Argentine ants were 2 times as diverse as those in California ants. As a result, the California ants recognize individuals. Argentine ants up and down the coast are close kin (relatives probably a better word), while from those different nearby colonies in Argentina were not closely genetically related. Basically, the genes are similar among California ants because they are descended from a relatively small initial population. Put more simply, the super-colony that occurs in California is in fact a single big colony.

Because it does not sting or bite, the Argentine ant is not a direct threat to humans, unlike harvester ants or fire ants. However, since there is little competition between opposing colonies of this species (one giant colony), this ant is the dominant species in areas where it becomes established. It is very aggressive toward other species of ants, and tends to out competes and replace other ants that are found in their same general area. As a result the Argentine ant is the major nuisance pest in urban areas, especially where there is an availability of water. These ants exist in backyards at high densities and are frequently associated with landscape features that provide favorable microclimates, such as potted plants and walkway, bricks, or stones. They enter homes through cracks and other spaces in search of food or water.

Argentine ants are also an economic threat because of their frequency of tending plant pest insects, such as mealybugs, scales, and aphids. In return for sweet honeydew secretions from these plant feeding insects, ants provide protection from natural enemies. Argentine ants may even move pests to better food sources or more favorable microclimates to maximize honeydew production. This mutualism can compromise management of pest insects by otherwise effective natural enemies. Thid can occur through removal or intimidation of predators and parasitoid wasps, leading to higher pest densities and greater plant damage than would occur in the absence of Argentine ants. Reportedly, parasitism rates of an important citrus pest, the California red scale (Aonidiella aurantii), were reduced 2 to 5 fold in the presence of Argentine ants.

Argentine Ant Control. There are no known specific enemies of the Argentine ant. Therefore, control is primarily accomplished by chemical and cultural means. Broadcast spraying of insecticides is of limited value because at any one point in time, the majority of the ant colonies are below ground where insecticides do not penetrate. The seasonal pattern of Argentine ant infestations in California and other states varies depending on geographic location. In Southern California they are warm season pests while in Northern California they are cool season pests. Application of residual insecticide and use of toxic baits are the principle means of Argentine ant control. Ideally, chemicals should be used early in the season while the colonies are rapidly growing and searching for food that is needed for their development. Reducing colony growth early in the season will typically result in lower populations later in the season.

In order to achieve an effective barrier for Argentine ant control, a residual insecticide must be applied as bands along the foundation, margins of sidewalks and pathways, around lower trunks of trees and garbage cans and other locations that serve as nesting sites for these ants. Generally, speaking, at maximum labels rates, a thorough application of such products can result in 8 to 10 weeks of control.

When using toxic baits, this should begin early in the season when egg production is at its peak. Protein based bait are likely to be most effective at this time: protein is needed at this time for the queen to produce eggs. Since this species co-mingles between nests, control with baits is especially effective for Argentine ant control. Reportedly, it is estimated that in 5 days, the exchange of ants between close colonies can be as high as 50% of the workers. As a result, baits consumed by workers of one colony will readily be spread to neighboring colonies.

The foraging range and behavior of these ants also pose a problem for baiting attempts. Reportedly, they will forage up 236 feet for available food. This equates to several homes in an urban environment suggesting that area wide treatment may be needed for good control. A number of the commercially available baits either are not attractive to Argentine ants or kill them too quickly, thus preventing foragers to return to their nests and thus sharing the baits with nest-mates. Liquid baits are considered to be the most effective way to control this species. These baits contain active ingredients that are effective a low concentrations. Another challenge in using baits for control of Argentine ants is their site fidelity for trail following. The problem is how to redirect them from following a pheromone trail.

Reportedly, aromatic cedar mulch has a degree of promise for use in IPM programs for the control of Argentine ants. It is both a toxicant and repellent to these ants. Landscaping mulches, such as pine straw, provide ideal nesting locations for Argentine ants while cedar mulch is not only a repellent to these ants but lethal when they merely walk across it. However, recent research indicates that trap mulching system provides limited benefits to Argentine ant management.

Crazy Ants (Paratrechina longicorni)

This species is very morphologically distinctive in that it is not misidentified in collections. Workers of this species are quite small with dark brown to black head, thorax, and gaster. The rest of the body often has faint a bluish iridescence. The 12-segmented antennae are extremely long and lack a terminal club.. The scape (second segment attaching to head) is exceptionally long and when pulled backwards will extend half its length past the posterior margin of the head. All workers are monomorphic and with a single node.
Crazy ant. Image courtesy April NobIle.CC BY-SA 3.0

This species occurs in many parts of the world and is not native to the United States (U.S.). However in the U.S. this ant is widely distributed from Florida to South Carolina and west to Texas and beyond. It is commonly  found in structures over much of the eastern U.S. and in California and Arizona. They are also reported from Virginia, Hawaii and Missouri, with isolated populations in Buffalo New York and Boston. Actually it has been suggested that that this species is the most broadly distributed of any ant species with the possible exception of the Pharaoh ant.

The stinger is lacking,  but crazy ants can bite and subsequently inject formic acid secretions onto the wound. Species confirmation can be accomplished via a hand lens due to the extremely long antennal scape and long legs The slender-bodied, long-legged workers are capable of extremely rapid movement.

Crazy ants commonly occur is large number in homes or out-of-doors. Workers forage long distances from their nests; as a result their nests are often difficult to locate and therefore control. As it common name indicates, it exhibits characteristic erratic and rapid movement. This species does not forage in trails as with many other species of ants. Even though the term crazy ant is officially identified with this species, there are other closely related ant species that are also called "crazy ants."

The crazy ant is both an agricultural and household pest in the tropical and subtropical, and is also a common indoor pest in temperate areas. It can successfully survive in artificial and highly disturbed areas including ships at sea. As a result of its ability to thrive indoors, there is no limit to where it can exist and has been reported from as far north as Sweden, and as far south as New Zealand.

Workers of this species are quite omnivorous and will feed on a wide variety of matter, including fruits, plant exudates, honeydew, household foods, live and dead insects, and seeds. This species successfully thrives in places such as gasoline stations, convenience stores, and sidewalk cafes. During the summer crazy ants exhibits a seasonal preference for a high-protein diet. As a result, during these months they may avoid honey or sugar baits. However, in the spring months they readily feed on honeydew produced by various Homoptera insects. Large prey items are carried by a highly concerted group actions.

Large Yellow Ant (Acanthomyops interjectus

Citronella ant workers measure about 1/8 inches long and are bright yellow to orange-yellow in color. The winged reproductives measure 1/4 inch long (not including the wings) and are glossy brick-red to brownish-red in color. The workers are monomorphic with a single thick node. The compound eyes of the workers appear disproportionately small. Although no stinger is present, these ants will bite and readily spray a pungent-smelling citronella (lemon-like) smelling chemical, hence their name. This odor is very noticeable when the ant is crushed.

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Image: large Yellow Ant. Image courtesy of April Nobile CC BY-SA3.0

Acanthomyops interjectus, the larger yellow and Acanthomyops clavinger, the smaller yellow ant, are found through  out the continental U.S. (U.S.).

This species typically lives outdoors in stumps, old logs, and under stones and boards. As a result, workers are rarely found indoors. They feed nocturnally, mainly on honeydew. Nest problems with larger yellow ants usually occur in the late summer and fall when mixed colonies of winged swarmers and wingless worker ants move toward buildings and enter through cracks or gaps in foundations. The temporary move indoor in winter, when nests are located somewhere in basements, under loose bricks or boards or in cracks in walls or floors. The ants do not forage for food in the house and apparently cause very little damage except to create piles of dirt at the entrance to the nest. Reportedly, these ants try to return to outdoors in the early spring if left undisturbed.

These ants are normally only nuisance pests and remain unnoticed, only if swarming reproductives enter homes through cracks in slabs or under or around door openings. These intrusions could possibly be of concern to homeowners; however, the ants will not reproduce within the home nor will they attack stored products in structures. In a limited number of situations, swarms may occur repeatedly and in such cases colonies may be located and destroyed by injecting insecticides into the nest openings. Colonies typically nest in soil.

Leaf Cutting Ants (Atta texana, Acromyrmex versicolor)

Atta texana can be readily identified by 3 pair of spines on the top of the thorax and a pair of spines on the head. The antennae are 11-segmented with a well-developed club. The body color is typically dull dark brown to rust brown. Acromyrmex versicolor closely resemble Atta texana, but differs in that they have 4 pair of spines on the thorax. Texana leaf cutting ants are found ranging from Texas eastward into Louisiana and south to Mexico. A. versicolor occurs from Texas into southern California. These are commonly found in many New World tropical areas. In such areas, columns of these ants frequently can be seen crawling up the trunks of trees and cutting small discs from the leaves. In some areas, these insects are so common that they become major agricultural pests.

Images leaf cutting ants carrying leaf discs. Courtesy Dr. Kaae

Some of these ants exhibit polymorphism (different form within a caste –in this case the workers) to an extreme. There are 4 different forms within the worker caste, namely the minima, minors, media and maxima. The minima are the smallest form of the adults and function to care for the brood (larvae and pupae) and fungal gardens. Media workers forage for and carry the leaf discs deep into their nests, where they are licked, cut into smaller pieces, dampened with an anal secretion and finally formed into a bed of moist pulp. The newly formed beds are then planted with fungi from established beds. As the fungus grows, it is harvested and fed to the larvae. Most leaf cutting ants are quite particular and typically cultivate and harvest only a single species of fungus. Media workers continuously ‘weed out’ any alien species of fungi that infest their gardens. It is believed that a few species actually produce fungicidal substances from their salivary glands which chemically aid in the weeding process. In some species when the swarming queens leave the colony, they carry the strands of fungi with them in pouches below their heads. Once new colonies are begun, the strands are ‘planted’ to assure a new garden of the correct species of fungi. The maxima are the largest of the forms with enlarged heads and protruding mandibles. These of course are the soldiers of the colony, functioning to protect the colony against intruders.

In a few species of leaf-cutting ants the minor caste performs a rather specialized function. These smaller workers frequently accompany the larger foraging leaf gatherers; they do not assist in leaf cutting; but ride back and forth to the nest either on the leaf portion or on the thorax of the media. Their sole function is to protect the media by snapping their mandibles at a species of parasitic fly that attempts to lay eggs on the media’s head.

Leaf cutting ants can do considerable damage to agricultural and urban plants due their forging activity. Some Atta species are capable defoliating an entire citrus tree in as little as 24 hours. In addition their nest making activity can be damaging to roads and farmland. A nest may cover from a foot to over an acre in size. The nest of this species consists of a number of connecting chambers 15 to 20 feet deep. Lateral foraging tunnels radiated outwards of 400 to 500 feet from a central cavity. There were numerous characteristic crater-shaped mounds spread though out the area. Foraging occurs primarily in the fall at temperatures between 45 and 90 F. Well-established trails typically link out to the plants being attacked.

Little Fire Ant (Wasannia auropuntata)

The little fire ant is tiny (approximately 0.04 inches in length) and reddish to golden brown. The petiole is hatchet shaped, with a node that is almost rectangular in profile. The thorax bears one pair of spines. The antenna is 11 segmented with the last 2 forming a distinct club. The head and thorax are heavily sculptured with grooves and pits. The erect body hairs are long, coarse and rather sparse.

Little fire ant with distinctive rectangular nodes on petiole.Image Courtesy Plegadis Public Domain.

In the U.S., this species occurs mainly in Hawaii and Florida, but more recently has been discovered in S. California.

Nests contain multiple queens and immatures (pupae, larvae, and eggs) and workers. Colonies of this species are frequently located found under rotten limbs, stones, leaves, loose bark or clumps of grass. This species is quite adaptable to nesting in both shaded and open areas and thrives well under moist or dry conditions. However, with excessive rain, they commonly relocated into buildings or trees. This species is well-known for its painful and long-lasting sting. In agricultural situations, these ants are frequently found on most parts of plants, including leaves, around fruit and on the trunk. These locations, its presence can result in frequent stings to workers. Indoors this species may infest clothing, beds, furniture, or food, especially fats, peanut butter, and other oily materials. Outdoors they readily tend honeydew producing Hpmoptera  and are predatory in nature. Trails of foraging workers occur along sidewalks, foundations and up the sides of buildings. Indoors trails of can be found along baseboards and under the edges of carpeting.

Odorous House Ant (Tapinoma sessile)

Workers are momomorphic and about 1/8th inches in length. Their color varies from dark brown to shiny black. Characteristically, their single node is not visible when viewed from above. From a side view, their thorax is uneven in shape. When crushed,a strong, rotten coconut smell is quite evident.
Image odorous house ant. Image Courtesy Antweb.orb, April Nobile CC BY-SA 3.0

Distribution. This species is widely distributed in North America.

As with many ants, this species is both a predator and scavenger that will readily consume most household foods, with a preference for those that contain sugar. In structures, they commonly nest near sources of insulation or heat. In especially dry of hot locations, nests have been found in the lids of toilets and house plant, thus seeking a degree of humility. Outdoors they are frequently found under rocks and exposed soil. The odorous house ant is apparently quite adaptable and forms colonies virtually anywhere in a variety of conditions. They are capable of foraging considerable distances from the nest (though their trails are rarely longer than 50 feet), but especially so along landscape edges. Colonies size is quite variable ranging from 100 to10,000 workers and less than  a dozen queens. In some situations, there may be as many as 200. A queens is capable of producing a few dozen eggs a day, but more commonly produces a few eggs a day over long periods. Their life cycle (egg to adult) is 34 to 38 days.

Odorous house ants attend aphid, soft scales and other honeydew producing insects. As with many species of ants, this species invade homes after heavy rain, possibly as result of washing away the honeydew, one of their main food sources. Little is known about the biology of this species although queens can live at least 8 months or longer, and workers at least a few months. As with most species of ants, males appear to live only around a week. Odorous house ants are not aggressive and typically do no sting or bite.

Their nests are relatively shallow and commonly occur in soil under wood, stones, bricks, or debris. Indoors they occur in a variety of habitats, , including wall voids, wooded structures and around water heaters and pipes.

Pavement Ant (Tetramorium caespitum)

Workers of the pavement ant are dark brown to blackish and 1/8th to 1/4th inch long. Their legs are distinctly lighter in color than the head or thorax. It is distinguished by 2 small backward projecting spines on the poster of the thorax, 2 nodes on the petiole, and grooves on the head and thorax. The antennae are 12-segmented, with a 3 segmented terminal club

The pavement ant is native to Europe, but was introduced to North America in the 18th century. Pavement ants are now distributed throughout the continental U.S., especially along the West Coast. In the Northeast and Midwest, it is considered the number one ant pest in commercial buildings.

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Pavement ant characterized by head  and thorax sculpture by parallel grooves.Image courtesy of April Nobile CC BY-SA 3.0.

In the early spring, colonies tend to expand and conquer new areas and as a result, frequently attack other nearby colonies; it is not unusual to observe huge sidewalk battles, ultimately leaving thousands of dead ants. This species frequently invades and colonizes seemingly impenetrable areas. During the summer. they dig out the sand in between the pavements to ventilate  colonies. They will eat almost anything including seeds, honeydew, honey, bread, meat, nuts, ice cream and cheese. They show a preference for meats and grease. They also feed on the pollen collected by ground nesting bees. They are particularly harmful to pollinating ground nesting bees such as alkali bees and will actively attack, and kill adult bees in order to reach bee’s larvae and pollen. In their attempt to procure plant sap, pavement ants can girdle and kill such plants as tomatoes, cabbage and carrots.

Pharoah Ant (Momomorium tsushinae)

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Right image: Pharoah ant, courtesy of April Nobile/  Right image: Pharaoh ant on sugar granule, courtesy of Julian.szulcc Wikimedia Commons

The origin of the pharaoh ant has not been well established, but possible locations include West Africa and Indonesia. This species has been introduced throughout most of the world. They are a tropical species but can survive and thrive anywhere, even in regions provided with central heating.

This species is a serious pest in rest homes, hospitals, hostel, houses, apartments, grocery stores, food establishments and other buildings. Their diet includes a wide variety of items, including juice, corn syrup, honey, jelly, baked goods, shortening, peanut butter, soft drinks, grease, toothpaste, dead insects, and even shoe polish. They can also chew holes in rayon, silk, and rubber goods.

Each colony generally produces sexually reproductive individuals twice a year. However, colonies raised in a laboratory can be manipulated to produce reproductives at any time of year. Colonies proliferate by "budding” (also called "satelliting" or "fractionating"). This process occurs when a portion of the colony leave the main colony for an alternative nest site.

Pharaoh ant colonies appear to prefer familiar nests to novel nests when budding. This suggests the ability for colonies to remember certain qualities of their living space. However, if the novel (unfamiliar) nest is of superior quality, the colony may initially move toward the familiar, but will eventually select the unfamiliar. The colony seems to assume the familiar nest is preferable, unless they sense better qualities in the novel nest. This so called decision-making process seeks to minimize the time the colony is without a nest while optimizing the nest the colony finally chooses.

The number of available budding locations has a large effect on colony fragmentation. A large number of bud nests results in small colony fragments, indicating that the colony has the ability to control size and caste ratios. Reportedly, a minimum group size of 469 individuals appears to be preferred by the species. Amount of fragmentation does not have any effect as far as food distribution. After budding, nest units do not compete for resources, but rather act cooperatively.

Pharaoh ants use a positive feedback system of foraging. Each morning, scouts will search for food. When these forager finds an acceptable food source, they will instantly return to the nest. This reasults in several ants to follow the successful scout’s trail back to the food source. Soon, a large group will reach the food. Scouts are thought to use both chemical and visual cues to remain aware of the nest location and find their way.

Even though M. pharaonis is most often thought of as an indoor pest, foraging has been found to be more prevalent outside. Even inside, colonies were found to forage close to windows, possibly indicating a propensity for outdoor environment.

Pharaoh ants have a sophisticated strategy for food preference. They implement 2 related behaviors. The first is known as satiation. The workers will at first show a strong preference for a particular food type. However, if this food is offered alone with no other options for several weeks, workers will ultimately show a distinct preference for a different type of food. In this way, the ants become satiated on a certain food group and will change their decision. The second behavior is called alternation. If given the continuous choice between food groups, Pharaoh ants will tend to alternate between carbohydrate-rich foods and protein-rich foods. These satiation and alternation behaviors are beneficial. The decision to vary the type of food consumed ensures that the colony maintains a balanced diet.

When social ants encounter ants from another colony, behavior can be either aggressive or non-aggressive. Aggressive behavior is very commonly seen; the attacking worker usually bites the opponent at the petiole. In non-aggressive behavior, antennation occurs when the 2 ants meet. In the case for Monomorium pharaonis, behavior is almost always non-aggressive even when the ants are from different colonies and of different castes. Very few cases exist where aggressive behavior is seen in these ants.

Budding is a major factor underlying the invasiveness of pharaoh ants. A single seed colony can populate a large office block In less than 6 month, almost to the exclusion of all other insect pests. Elimination and control are difficult because multiple colonies can divide into smaller colonies during an extermination programs, thus increasing the chance of  repopulation at a  later date.. Pharaoh ants are a major hazard in hospitals, where their small size means they can access wounds and medical instruments, causing the spread of infection and electrical interference.

Control of Pharaoh Ants. Based on research, several important points about control of these ants have been discovered and include:

1. Baits are the only effective method of cotroling or eliminating this pest.

2. Fast-acting residual insecticides should not generally be used in Pharaoh ants control; as indicated, this results in colony budding (formation of new nests).

3. The use of fast acting insecticide can also contaminate bait stations and typically only kills foraging ants.

4. If bait switching in Pharaoh control is attempted, populations should first be monitored for changes in food preferences.

5. Insect growth regulators (IGRs-Pharaorid) allow for more inter-colony transfer of baits than use of metabolic inhibitors which are more localized in their effect. Metabolic inhibitors tend to be fast acting while IGR are slower acting, thus allowing transfer of bait within a colony.

7. For structural infestations where Pharaoh ants are foraging inside and outside a structure. the use of baits outside the structure is sufficient to attain control.

For proper placement of baits, trails and resources (both food and water) should be located. In an apartment complex infested with these ants, residents should be interviewed. This will not only help in determining where ant activity has been observed, but will give the applicator a chance to explain to the tenant about the baiting program. A dab of honey placed on index cards that are placed around the structure can be used to survey possible locations of the ants. The cards are typically placed in food and water locations around (kitchen, laundry, lounges) the individual units, as well as outside and in offices and the lobby of the apartment complex. Up to 16 of these baited cards should be placed in each apartment, usually 2 to 4 each in the kitchen, bedroom, bathroom and living room. These cards should also be placed in locations where the residents have observed ant activity. Window sills are ideal locations for these bait card in the living rooms and bathroom. Insects fly to light from widows and eventually die.  As a result, Pharaoh ants feed on these dead insects and commonly nest in the cracks and crevices around window casings. In kitchens and bathroom bait card should be placed near water sources (pipes, faucets, sinks, bases of toilets, drains, counter tops). Outside cards should be places near doors, windows and plumbing lines. It is important to position the cards along edges or other structural guidelines that the foraging ants follow. These cards should be left in place long enough for the ants to find the baits and subsequently recruit other forages. This may take up to several hours for this to occur. The number of ants found on each card should be estimated and recorded on an inspection diagram.

This type of  pretreatment survey allows the applicator to determine where the majority of ant activity is and therefore determine where toxic baits should be located. Monitoring will also assist in finding small nests of these ants which might otherwise overlooked and be a source of reinfestation. Following foraging ants returning to their nests from the bait cards can be used to locate points of entry from the nests into the units. Such entry points should be noted on the inspection diagram and toxic baits should be placed at these locations. Because foraging Pharaoh ants follow wires and pipes to trave,l baiting every switch plate and pipe void is recommended. Baiting outside is also important. A considerable amount of Pharaoh ant foraging occurs outdoors in warm weather.

Harvester Ants (Pogonomyrmex spp.)

Of the 23 species that occur in the U.S., 22 are found west of the Mississippi River.

These (Pogonomyrmex spp.) ants are commonly thought of as the large red or black ants that form rather large nests in open fields, schoolyards, along railroad tracks, alleys or other similar situations. These large ants are characterized by the presence of fringes of long curved hairs on the  underside of the head. These hairs are used to clean the ant’s antennae and legs, carry water and remove sand during excavation of their nests.

Black harvester ant with long hairs below head. Image Dr. Kaae

The nests typically are quite large, consisting of 1 or more holes surrounded by a low flat crater (up to 8 inches across). This crater is surrounded by a rather large vegetation free area. Harvester ants feed primarily on seed. In agricultural areas they are considered beneficial as they remove weed seeds from crops. The main reason they are found along railroad tracks is due the grain that is lost during seed transportation.

Harvester ants readily sting but typically are not aggressive, unless defending the nest. If disturbed, they will swarm from the nest and readily sting. Their venom is extremely powerful resulting in considerable pain that may last for several days. Harvester ant venom is the most toxic venom found in arthropods although there is considerably less in a sting than in black widows; consequently, the sting of the ant is much less dangerous than the bite of the spider. These are the ants that are commonly used in ant farm.

Fire Ants

The fire ant, Solenopsis geminata, is a native U.S.species that sometimes is referred to as the tropical fire ant. It ranges from South Carolina to Florida and west to Texas. It is very similar in appearance to the southern fire ant, except its head is much larger and the petiole node is higher and narrower. This species usually nests in mounds constructed around clumps of vegetation, but may also nest under objects or in rotting wood.

Black Imported Fire Ant.

The black imported fire ant, Solenopsis richteri, is very similar to the red imported fire ant. Its current distribution is limited to a small area of northern Mississippi and Alabama. It may be displaced from established habitats by the red fire ant. Scientists have long thought that the black and red fire ants were 2 distinct species. Recently, it has been discovered that hybrids of these ants produce viable offspring, and some scientists now wonder whether they are simply two races of the same species, varying in color and perhaps behavior.

Southern Fire Ant.

The southern fire ant, Solenopsis xyloni, is a native species that occurs from North Carolina south to northern Florida, along the Gulf Coast and west to California. In California, it occurs in the lower altitudes from Southern California up through Sacramento but is seldom found along the coast in central to northern California. This is probably our most common native species of ant, but its distribution is greatly retarded when the Argentine ant is present. However, in areas where the Argentine ant is controlled, populations of this species rapidly return.

Colonies may be observed as mounds or more commonly may be constructed under the cover of stones, boards, and other objects or at the base of plants. These ants also nest in wood or the masonry of houses, especially around heat sources such as fireplaces. Nests often consist of loose soil with many craters scattered over 2 to 4 square feet. In dry areas, nests may be along streams, arroyos, and other shaded locations where soil moisture is high. Southern fire ants usually swarm in late spring or summer.

The workers are very sensitive to vibrations or jarring. If their nest is stepped on they will rush out and sting the feet and legs of the intruder. Individual reaction to their venom is quite variable depending on allergic reaction. There is a least one case of a human infant death due to mass stinging of this species.

This species is practically omnivorous feeding on a variety of materials including honeydew, meat, seeds, fruit, nuts, cereal and cereal products, grease and butter, and dead and living insects. It can be quite detrimental to agriculture foraging for seeds from seed beds, girdling nursery stock, and consuming fruits and vegetables. In addition, these ants will remove insulation from wiring and occasionally gnaws on a variety of fabrics.

Red Imported Fire Ant (Solenopsis invicta).

The red and black imported fire ants were first reported in the U.S. in 1929. It is thought that they came to the port in some soil used as ballast in the bottom of a cargo ship. Since this introduction the black fire ant has not spread as rapidly as the red imported species. By 1953 (first official USDA survey), the red imported fire ant had spread to over 100 counties in 10 states. Today, it is prevalent throughout the southeastern US and has moved into Texas, New Mexico, Arizona, and California.

In Southern California, state and federal officials have placed Orange County and portions of Los Angeles County and Riverside County under quarantine. The quarantine limits the movement of articles including plants and soil, and requires commercial nursery growers to take steps to ensure their products are free of Red Imported Fire Ants. It is believed that the infestations in southern California may stem from the shipment of infested nursery stock from the southeastern states. Fruit orchard infestations in the agricultural regions of California's San Joaquin Valley have been traced back to colonies that hitchhiked on beehives shipped to California from Texas.

The natural movement of fire ants is limited to mating flight or by rafting during period of flooding. However, the rapid movement of these species across the South and westward is mainly associated with human activity.  In this case, the initial spread of these ants in the southeastern US was thought to be due to movement of sod and potted ornamental plants. This inadvertent movement of S. invicta and S. richteri was noted by the U.S. Department of Agriculture in 1953 when a direct link was established between commercial plant nurseries and the spread of imported fire ants. In response to mounting public pressure, the U.S. Congress appropriated $2.4 million in 1957 for control and eradication efforts. As part of an overall plan, quarantine was imposed to retard or prevent the artificial dissemination of these now notorious pests. On May 6th 1958, regulations governing the movement of nursery stock, grass sod and some other items were instituted through the Federal Quarantine 301.81. By that time, however, imported fire ants had moved into 8 southern states. This spread, although slowed considerably by federal regulations and climatic conditions, continues even today. In recent years, isolated infestations of imported fire ants have been found as far west as New Mexico, Arizona California and as far north as Kansas and Maryland. In the case of California it is thought that the spread of these ants into this state was due to movement of bee hives as most initial infestations were found in around orchards and other situations where bees were moved into these areas for crop pollination. Based on USDA prediction these ants have a potential of even expanding the spread throughout much of the U.S. 


Range expansion legend .

Image: current and potential distribution of imported red fire ant. Courtesy of USDA.

Adult fire ants (Solenopsis spp) are characterized by the presence of a 10-segmented antennae, 2-segmented antennal club and 2-segmented waste that joins the thorax to the abdomen. Species identification is somewhat more difficult due to hybridization between the 2 "native" species


Diagram of diagnostic characteristics of red imported fire ant. Courtesy USDA

A mature colony of fire ants typically consists of 4 main stages: egg, larva, pupa, and adults. Since these are true social insect, there is a caste system with different shaped and sized adults that carry out different function within the colony. These adult forms include the polymorphic workers, winged males, winged females and 1 or more reproductive queens. The egg, larval, and pupal stages occur within the underground nest and are only seen when nests are disturbed or when they are being carried to a different location by workers. The eggs are small but can be seen with the unaided eye. They hatch into the grub-like legless larvae that are fed by the workers. Ant larvae in general are legless, carrot shaped with a well-developed unpigmented head capsules and are typically hooked at the head end. The larvae will grow and molt (shed their exoskeleton) three times prior to molting into the pupae, which are similar in appearance to the adults except that their legs and antennae are held tightly against the body. As with the larvae, the pupae lack pigmentation, especially in the early instars. As they mature they begin to turn darker. As discussed in honeybees, the function of the polymorphic workers is determined primarily by age (and to a much lesser degree by size). Younger workers typically care for and feed the brood; middle-aged workers maintain and protect the colony. The oldest workers forage for food.

Egg, larval and pupal stage of fire ants. Courtesy of USDA archives

Worker fire ants carrying larva for relocation. Courtesy of USDA

The alates, or winged reproductives, are most abundant in the late spring and early summer, but can be found at any time of the year. The males are decidedly smaller than the females, glossy black and have a smaller head. Although both winged males and females can be found in the same colony, as a general rule one form will be dominant. It is possible that this functions to increase the chances of one sex mating with another from a different colony. Most colonies in a given area typically swarm on nuptial flights at the same time. This benefits the species and insures mixing of the gene pool. It is well-documented that inbreeding is generally detrimental to a given species.

Winged reproductive of the red imported fire ant. Image courtesy of USDA archives

Mating flights most often occur at mid-morning 1 or 2 days following a rainfall if the temperature is above 22°C and the wind is light. At this time a virgin female flies into a cloud of congregating males and mates in the air. The male subsequently dies while the female seeks a location to start a new colony. Once located, she breaks off her wings and excavates a brood chamber approximately 1 to 2 inches below ground. The new queen subsequently deposits a few dozen eggs which hatch in a little over a week. The queen does not forage but feeds the first generation of larvae from nutrients obtained from her fat reserves and by dissolving her no longer needed wing muscles. The larvae obtain the nutrients by trophallaxsis (exchange of alimentary fluids) or from sterile eggs she has produced for that purpose. The entire life cycle is completed in 3 to 4 weeks.

The initial generation of adult worker (minims) are relatively small due to a limited amount of nutrients available from the queen. Once developed these worker open up the brood chamber and begin to forage for available food. Soon another generation of larger adult workers has developed and the colony begins to grow. Workers start to emerge daily and within six months the colony population approaches several thousand and an above ground mound is visible. The polymorphic (poly in Latin means many and morph means form) nature of the worker becomes more apparent. The largest workers in the colony (majors) can be as much as 10 times the size of the smallest workers (media). The queen lives up to 7 years and produces an average of 1600 eggs per day. At maturity, a monogynous (one queen) fire ant colony can consist of over 250,000 ants. As discussed above, some fire ant colonies have only one queen per nest while others can have many queens and are called polygynous colonies. The polygynous colony may be more difficult to control because all the queens must be killed to prevent the colony from; ssurviving. Polygynous colonies frequently expand by "budding"; some of the queens and workers break off from the parent colony and start a new mound nearby. This process in polygynous colonies can accounts for much higher mound density which sometimes approaching 1,000 mounds per acre.

Image: different sized worker adults. Courtesy USDA archives

One of the identifying characteristics of an imported red fire ant colony is the earthen nest or mound. This mound is a cone-shaped dome with a hard crust. They averages 1 ½ feet in diameter and 8-inches in height. In heavy clay soils they can exceed 3 feet in height and 4 1/2 feet diameter. There are usually no external openings in the mound; but tunnels a few inches below the surface tunnels radiate several feet from the mound allowing foraging workers access to the colony. These mounds serve several functions:  They act as a flight platform for nuptial flights and to raise the colony above ground in excessively wet soil while protecting it above ground from intruders and rain. They also serve as a passive solar collector to supply warmth to the colony during the cold winter months.

Image: red imported fire ant mound. Courtesy of USDA archives

In areas with hot, dry summers these mounds may not be maintained or may not be formed at all. In a dark, protected site with sufficient moisture and an adequate supply of food, fire ants will nest in a wide variety of locations (e.g. rotten logs, walls of buildings, under sidewalks and roads, in automobiles, in dried cow manure).

Economic Impact. Fire ants are omnivorous, feeding on almost any plant or animal material; although dead and living insects seem to be their preferred food. In rural habitats, they have a major impact on ground nesting animals (birds, reptiles, mammals). Studies have shown that once established in a new area there is typically a minimum of a two-fold reduction in the populations of field mice, snakes, turtles and other vertebrates and a maximum of a total elimination of some species. Fire ants also feed on plants attacking young saplings and seedlings, destroying buds and developing fruits and have been shown to feed on the seeds of over a hundred species of native wildflowers and grasses.

Damage to plants is increased during periods of drought as fire ants seek alternate water sources. In fields where drip irrigation is used, these insects build their mounds over the emitters reducing or blocking the flow of water to crops. In some cases, actual physical destruction of microsprinkler assemblies has occurred. Finally, the mere presence of fire ants on plants and within the field will deter hand-harvesting of crops.

As an urban pest, imported fire ants cause many of the same problems experienced in rural areas. In addition, they nest within the walls of homes and offices. Colonies are established under sidewalks and roadways frequently resulting in complete collapse of sections of these structures if the nests are eventually abandoned. The presence of fire ants can deter outdoor activities in yards, parks and school grounds. Home invasions can threaten small children and the elderly. House invasions are especially prevalent during periods of heavy precipitation and flooding. Fire ant colonies have been found inside automobiles, trucks and recreation vehicles resulting in traffic accidents caused by fire ants stinging the drivers. Imported fire ants are attracted by electrical currents and have caused considerable damage to heat pumps, air conditioners, telephone junction boxes, transformers, traffic lights, and gasoline pumps.

Because of their reputation, people fear fire ants. In some areas playgrounds, parks, and picnic areas are rarely used because of the presence of fire ants. In campsites of state and national parks in fire ant infested areas, it is often difficult to put up or take down a tent without being stung by angry ants.

Fire ants are best known for their behavior of stinging, frequently in mass. If a nest is disturbed hundreds if not thousands of ants will quickly emerge and attack the intruder. This occurs so quickly and in mass that is not uncommon to have hundreds on the victim before the first sting is felt. To make matters even worse a single fire ant can sting repeatedly and will continue to do so even after their venom sac has been depleted. Once reaching the victim the ant will typically attach with its mandibles to the skin and then insert its stinger. Subsequently, it will rotate it abdomen and repeatedly sting using the attached head as a pivot.  The result is a circle of several stings from the same ant.

Initially, the sting(s) result in a localized intense burning sensation (hence the name "fire" ant). Within a day or two a white pustule forms at the sting site. Pustule formation occurs only with the red and black imported fire ant and not the southern fire ant or fire ant. There is a possibility of secondary infection and scarring if the wounds are not kept clean or if they are continually picked at or scratched. As with any other Hymenoptera stings, there are a few individuals who are hypersensitive to the venom and can react quite strongly and be severely affected. Symptoms in these cases can include chest pains, nausea, dizziness, shock or, in rare cases, lapsing into coma. In cases of an allergic reaction, even a single sting can lead to a potentially serious condition called anaphylactic shock. There are recorded cases of human death resulting from fire ant stings but these are rare.

Pustular formation for sting of red imported fire ant. Image courtesy of USDA Archives
Secondary infection of sting from red imported fire ant. Courtesy of USDA archives

Individuals with disabilities, reduced feeling in their feet and legs or reduced mobility, are at greater risk from serious stinging incidents and the incidence of resulting medical problems may be even greater. Large numbers of ants can sting and even overcome victims before they can safely escape. There was a recent case where fire ants entered a room of an elderly gentleman in a retirement hospital and basically stung him to death. In his case, he was unable to escape their attack.

Individuals who are known to be allergic to fire ant stings should seek professional advice from a physician or allergist, especially if they are in situations where they might be exposed to these pests. There are emergency treatment kits that are available (by prescription) for individuals who are sensitive to their sting. Fortunately, relatively few deaths from fire ant stings have been documented, especially when compared to deaths from bee and wasp stings. Victims stung to death by fire ants often were not able to escape, sustained large numbers of stings, and suffered allergic reactions to the venom.

Control. There are basically 2 methods of fire ant control, namely individual mound treatment and broadcast treatment. Before attempting either, it is advisable to check with regulatory agencies as the availability and use of different chemicals for either method may vary from state to state.  In addition, in many cases free control by state governmental agencies of these pests is available.

Individual Mound Treatments. Treating individual fire ant mounds can be time consuming, but it is generally the most effective method of control. Once treated it will take anywhere from a few hours to a few weeks before total elimination of a colony depending on the product used, time of the year and size of the mound. Treatment is usually most effective in the spring with the key being to treat all the mounds in the area. If control is not complete, reinfestation of an area can take place in less than a year. There are several different methods that can be used to treat individual mound

One of the more commonly used methods is drenching mounds with a high volume of diluted contact pesticide. As with any treatment, it is extremely important to follow label directions not only to attain maximum effect, but to maximize safety of the application and avoid potential illegal consequences. In most cases, the mounds and surrounding areas are wetted thoroughly, but gently, with the drench. Subsequently, the mound is broken open and the insecticide is poured directly into the tunnels. Mound drenches are most effective after rains when the ground is wet and the ants have moved up into the drier soil in the mound. During excessively dry weather, effectiveness of the treatment may be enhanced by soaking the soil around the mound with water before treatment. One problem with this technique is that the queen may be too deep to be reached with the drench. This may be especially true if the colony is disturbed prior to an application. In this case, the workers may move the queen deeper into the colony in order to avoid a potential threat.

Granular formulations are also available for individual mound treatment. In this case, once the recommend dose is applied to the mound it should be watered thoroughly in order to reach the worker ants and queen that occur deeper in the colony. The dissolved granules must come into direct contact with the ants to have any effect. As in mound drenches, care must be taken not to disturb the colony prior to application.

A few insecticides are marketed as injectants. In this case, they may be injected using a "termite rig" with a soil injector tip, a standard 1 to 3 gallon compressed air sprayer with a fire ant injector tip, or a special aerosol soil injector system. The mound is injected in a circular pattern, usually at 3 to 10 points. A new product combines insecticide treatment with high temperature vapors to increase penetration.

Fumigants are readily available in most states for fire ant control. These are usually more effective than surface applications or mound drenches, but are also more expensive and can be dangerous if not handled properly.

Depending on the state, a number of fire ant baits are available. These can be used for treating individual mounds or for broadcast treatment of larger areas. The bait should be uniformly applied around the mound 0.3 to 1.0 yards away and not on the mound itself. Baits are much slower acting than the control methods listed above but are generally safer, cheaper, and more effective in the long run.

The use of boiling water has been examined on several different occasions resulting in varying degrees of success. In one experiment, over a 50% of treated mound were eliminated by pouring approximately three gallons of hot water directly into the mound. The use of steam produced by a steam generator produced similar results. Regardless, both techniques are far less effective than the use of drenches, fumigants,  and granular formulation. Baits are cumbersome in the field are not practical when dealing with large populations of these pests. Area wide flooding with water has not proven to be effective, impractical in most situations and can led to spreading of the population due to the rafting ability of these insects.

Broadcast Treatments. A number of fire ant baits are commercially available for broadcast treatments (again depending on the state). Baits are composed of an inert carrier-attractant (corn carrier and soybean oil) and toxicant. The active ingredient (either a slow-acting insecticide or an insect growth regulator) is incorporated into the oil. These baits can be applied either by a hand operated granular fertilizer spreader or larger equipment. Once foragers find bait they carry it back to the nest, ingest it and begin feeding other ants in the nest. Because the active ingredients are slow acting, they are spread around the nest before the desired effect. This formulation and means of application has a number of advantages. Unlike individual mound treatments, colonies need not be "located" in order for them to be treated. As a result, this method is less time intensive and consequently less expensive than individual mound treatments. On the other hand, broad cast treatment has the potential of affecting non-target organisms. It is also slow acting and the effectiveness of the bait is greatly reduced when they come in contact with water from rain, irrigation or other sources. Finally, baits are only effective during those times of the year or temperatures when the ants are readily foraging. Generally speaking, it is advisable to only use this type of treatment in areas where there is little or no human traffic. If broadcast treatment is used in such an area, a good choice is growth regulator bait, which poses much less risks to non-target species. example, Fenoxycarb baits have been reported to be quite effective for suppression of fire ant populations when applied in one application over a wide area.

Carpenter Ants (Camponotus spp.

This genus contains the largest of our domestic ants, with the worker caste being highly polymorphic, The most common type of domestic ants that approach their size is the black and red harvester ants. When viewed from a dorsal angle these ants appear quite similar.

However, separation of these 2 groups is fairly easy from a side view. Carpenter ants have 1 well-developed, erect node on the top of the petiole, while the harvester ants have 2 less developed, rounded nodes. In addition when viewed from the side, the profile of the thorax of carpenter ants appears rounded and humpbacked.

Carpenter ants are of minor consequence in some areas of the U.S. and of major concern in others. Factors that appear to determine their importance are humidity, other sources of moisture and availability of wood, especially cut or fallen timber. Generally speaking, higher humidity is conducive to their presence and establishment. It follows that on the West Coast, carpenter ants are more of a problem in the Pacific Northwest than in Southern California. Similarly in southern California, they are more of a problem in the mountains than the lowlands. A few studies have indicated that these insects are more of a problem than termites in the Pacific Northwest. In this area, one study, which extended over a 5-year-period, 23 pest control companies reported treating 824 separate carpenter ant infestations. Other sources indicated that over a 21-year period, all existing homes in Washington State will have been infested with carpenter ants. This amounts to 21,900 infestations per year that are treated professionally. Also, it is estimated that homeowners treat an equal amount. This is not to say that the average pest control company does not deal with carpenter ants.

A queen in a mature colony may lay a dozen or so eggs a day. These eggs typically hatch in about 3 weeks and the entire life cycle from egg to adult may be completed in as little as 9 weeks. Of course, as with all insects, the rate of development of carpenter ants is totally temperature dependent. At 80 degrees F ,the life cycle may take 9 weeks and the same insect when raised at 60 degrees, may take several months to complete development.

In a mature carpenter ant colony, there are 3 basic castes, namely the queen(s), workers, and males or kings. The workers are sterile females and develop from fertilized eggs. In most species, there is a degree of polymorphism in the worker adults, meaning that there are different sizes of workers. When polymorphism exists, the larger workers typically defend the colony, and the smaller forms carry out other duties of the colony.

The number of each caste in a colony depends on the species and age of the colony. Very mature colonies may have between 3,000 and 4,000 workers. In the late spring or early summer in a mature colony, winged male and female ants swarm. These individuals have the potential of forming a new colony. If the female is mated, she will typically burrow beneath the soil, under a rock or into an old drywood termite gallery. At that point, she breaks off her wings, forms a small cavity and waits a few weeks for the eggs to develop in her ovaries. Her large wing muscles are then dissolved, passed into the blood,carried to the eggs and utilized in yolk development. Once the eggs mature, a dozen or so are deposited. Once the young hatch, the queen cares for and feeds the developing larvae on secretions from her salivary glands. Because the queen does not leave her nest during this time and does not feed, she can only feed the developing larvae from stored fats in her abdomen and dissolved wing muscle nutrients. The adult workers from this first brood are small and are normally referred to as the minimae. Once developed, these workers leave the nest in search of food and water and ultimately assume the duties of feeding the next generation of brood. By midsummer, the second generation has developed into workers. It generally takes 3 to 5 years for full development of a colony and the maximae (larger workers) are not produced until the third year. Swarming forms can be seen in the colony by the beginning of the second year.

As with other ant species, carpenter ants tend to form satellite colonies that are associated with their main colony. These colonies may be loosely connected via pheromone trails and it is not uncommon for ants from the satellite colonies and the main colony to intermingle and even transfer brood from one colony to another. Normally, brood is only moved from mature colonies to satellite colonies. This is a means of expanding the size of the overall colony (satellite colony plus main colony). Typically satellite colonies do not contain a queen, eggs or young larvae, but do contain older larvae, pupae workers, and winged males.

Foraging ActivityAs do many other species, carpenter ants forage with the use of trail following pheromones. When initially seeking food, individual ants forage at random; however, when an ant finds a good source, as it returns to the nest, it drags its abdomen on the ground releasing small amount of the pheromone (produced in its gut). Upon reaching the nest it shares the food with the other workers alerting them to the presence of the source. Once these ants leave the nest they follow and reinforce the chemical trail that leads to and from the food. The chemical itself is not long lived so the trail needs to be constantly reinforced by the foraging ants. This obviously serves to eliminate the problem of a trail eventually leading to a deplete. d source of food.

Carpenter ants forage primarily in the spring and summer months in temperate climates with peak activity occurring between 4 AM and 8 AM and 71 to 74 degrees F.  However, the time of day is going to vary depending on the geographical location and if the infestation is located indoors or outdoors. For example in warmer areas, outdoor infestations primarily forage any time of the day in the spring and fall when favorable temperatures exist. During the hotter summer months of July and August, they primarily forage during the night.

Only 2 to 3% of the total nest population forages at any one time. As a consequence, it does little good to spray for foraging workers. In fact, when the trails of many ant species are sprayed, thus eliminating the foraging workers, the colony becomes stressed. As a result, the colony tends to bud or form new queens and split up, thus forming the potential for an even heavier infestation.

In nature, the main diet of carpenter ants is honeydew. Aphids, leafhoppers, mealybugs, soft scales, and some of the other less known Homoptera insects produce honeydew. These insects suck the sap of leaves and other plant parts, but typically do not digest it all. The excess is passed from the anus in the form of honeydew or partially digested plant sap. Carpenter ants have a mutual relationship with these insects in which both parties benefit. Of course the ants benefit by obtaining food from the aphids and their relatives. The honeydew producing insects are guarded by the ants, which protect them from the many types of other insects that feed on them. The ants actually milk the aphids. It is not uncommon for an ant to approach an aphid and then stroke its abdomen with its antennae, resulting in the production of a drop of honeydew.

Carpenter ants feed on materials other than honeydew. Another essential component of their diet is insects, although they rarely,eat honeydew-producing insects. The protein the ants receive from this source is essential for brood production. Carpenter ants do not feed on wood, although some species can do considerable damage to homes when expanding their galleries.           

When carpenter ants are found foraging in the home, it does not necessarily mean that the main nest is found in the structure. A recent study indicated that in approximately 75% of the time when these ants were found foraging in the home, they originated from outdoor sources, with the most common location being dead trees. Of course, this figure would likely change drastically in more urban settings. Additional findings were that it was very common for carpenter ants to set up smaller satellite colonies within structures; however, these satellite colonies typically were connected to the large parent colonies that were located outdoors.

Outdoor colonies have little difficulty entering a home to forage for food. Studies indicate that old homes are as readily infested as new homes. These ants can easily travel through or on wall voids including insulation, heating ducts and water pipes.

Inspection. Inspection for carpenter ants should be based on a thorough understanding of the biology and behavior of these insects and should incorporate both indoor and outdoor locations. It is always advisable to thoroughly interview the occupants of the structure; they are likely to have a fairly good idea as the locations of the problems.

The most common locations where indoor nests of these ants are likely to occur are attics, window frames, floors, cedar/plywood siding, moderately sloped roofs, wall voids and crawl spaces. Keep in mind that situations that are favorable to carpenter ant infestations are areas of high moisture content (both inside and outside the structure), rotting wood with fungal infestations, vegetation in contact with the structure, homes without basements but with crawl spaces, homes with previous damage from wood destroying beetles and termites and trees stumps or downed trees on or near the property.

Carpenter ant nests are typically located within wood and therefore not readily visible. One means of detecting their location is to follow the foraging trails. Of course this is only possible if it is the right time of the year and day when these ants actively forage. Even if active, the trails themselves may not necessarily be readily visible. Outdoor hidden trails may follow the shallow roots of trees, occur under leaf litter and other debris on the ground, pass under patios and driveways and even occur as shallow tunnels just below the soil. However, more time than not ,the trails do occur above ground and are detectable. Above ground trails are frequently located immediately next driveways and lawns, the outside foundation of the house and even follow the natural contour of the ground. Once detected, it is advisable to note where the trails and nests are located. Studies indicated that 90% of reinfestations occur along previously used trails and in old nest sites.

Outdoor inspection should be thorough. The inspector should keep in mind that most structural infestations originate outdoors (primarily in tree stumps), either directly as foragers or as the main outdoor nest of indoor satellite colonies. A good indication of the latter is foraging ants carrying later instar larvae from an outdoor source to indoor satellite colonies. If more than 1 colony is found, it becomes important to determine if the ants come from the same group (e.g. main and satellite colony) or from different colonies. Ants from the same colony group will not fight but ants from different heritages will.

It may become important to distinguish wood damage due to carpenter ants from that caused by drywood termites or even subterranean termites. Carpenter ants frequently occupy abandoned or empty termite colonies. In this case, the galleries or tunnels of each appear very similar. As most pest control operators know, the galleries of drywood termites typically cross the grain and growth rings of the wood and those of subterranean termite more or less run with the grain and growth rings. In the case of carpenter ants, the walls of the individual tunnels take on a polished appearance.

Image: carpenter ant. Individual tunnel walls are cleaner and more polished than those of the 2 termite types. Courtesy of Jim Kalisch, Univ. Nebraska Entomology

When making an inspection, it may become necessary to distinguish between the types of frass produced by drywood termites and carpenter ants, as both expel this material from their galleries. In the case of drywood termites, their frass is pellet-like in appearance with the individual pieces about the size of a grain of sand. In the case of carpenter ants, the frass is shredded and typically contains insect parts.

Left image of drywood termite pellets. Courtesy of Forestry Images, Mohammad Del Damir.  Right image: carpenter ant frass mixed. University Nebraska Entomology
with insect parts. Courtesy of Jim  Kalisch, Univ. Nebraska Entomology

Finally, large colonies of carpenter ants are somewhat noisy. It is not uncommon to be able to hear their low level rustling in the walls. Some companies use the aid of listening devices for this purpose.

Prevention and Control Strategies. The degree of prevention and control needed of is partially depends on how extensive and persistent of a problem exist. Any or all of the following may be needed:

  1.    Adequate ventilation to reduce moisture in crawl spaces, attic and basements.

  2.    Elimination of ground wood contact.

  3.    Reduce vegetation contact with structure-reduces entry site for ants.

  4.    Chemical treatment of wall voids.

  5.    Proper vapor barriers in crawl spaces.

  6.    Adequate drainage leading water away from structure and reduction of other water sources that may lead to fungal infestations.

  7.    Reduction of stumps and other wood on premises that will support outside colonies.

Thief Ants (Solennopsis molesta)
Thief ant. Courtesy, April Nobile CC BY-SA 3.0

The name of this ant refers to their behavior of nesting close to other species of ant’s nests and consequently stealing their food. Another common name of this species is the grease ants because they are attracted to grease. S. molesta workers range from 1/32 of an inch to 1/8 of inches in length. Their color varies from tones of yellowish or brownish. They possess a 2-segmented petiole connecting their onlong abdomen to the thorax. The antennae are 10-segmented and terminate in large capitate club. Thief ants have small stingers and typically relativeluy small eyes. The worker caste possesses large jaws that function to carry food back to the colony.

Solenopsis molesta is native to the U.S. and is typically more common in the central states and east coast.

The range of habitats of this species is extremely diverse; it would appear that this species can survive just about anywhere. They readily nest in homes in a large variety of locations, including in cracks or under the floorboards. Common outdoor nesting locations are under rocks, in any exposed soil, and rotting logs. In the absence of suitable habitats, they move into and take over colonies of other species. Their nests are typically large (few hundred to a few thousand workers) and have tunnels that lead to satellite colonies; this insure a reliable and steady food source. The size of an individual colony is somewhat dependent on its location. Colonies that exist in a location with a reliable food source typically are relatively small owing to that lack of the need for a large numbers of foragers. Because these ants are so small, they can colonize just about anywhere. They can even exist in homes without the residents even knowing that the problem exists. In addition due to their small size,hey can easily enter sealed packages of food. They will eat just about anything, including dead animals, and are capable of foraging considerable distances in search for food. They readily forage in trails.

Mating typically occurs in midsummer through fall. Once mated queens sometimes fly with a worker or two clinging to their bodies, presumably to aid the queen once she locates a suitable location to start a new colony. Queens are quite prolific and are capable of depositing eggs with a range from 27 to 387 eggs per day. The entire life cycle from egg to adult worker is around 50 days depending on the temperature. Besides grease, these ants are drawn to and consume cheese, meat, other dairy products, and seeds. They are also predatory consuming larvae and pupae of other ant species. They will also consume fruits and sugary soft drinks even though they are not readily attracted to sweets. Because of their inaccessible, remote nesting areas and extremely small size, it is often extremely hard to locate colonies of this species in structures. The easiest way to locate a colony is inspect for trails of ants. It is also hard to get rid of a S. molesta infestation because they are not attracted to common ant baits.

Velvety Tree Ant (Liometopun occidentale)

File:Liometopum occidentale casent0005328 profile 1.jpg
Velvety tree ant. Courtesy of April Nobile. CC BY-SA 3.0

Velvety tree ant workers are monomorphic and about 1/16 to 1/4 inches in length. The abdomen is velvety black to brown, thorax yellowish red and the head is black dorsally and reddish on the bottom. The antennae are 12-segmented without a club. The thorax lacks spines and is evenly rounded when viewed from a lateral angle. the pedicel is 1 segmented. As their name implies, they have an abundance of body hair or setae giving them a velvety appearance.

The velvety tree ants are found in the western and southwestern states from Colorado through Arizona, California and the Pacific Northwest.

These ants in their natural habitat are typically found under rocks and in rotting trees. Common nest locations are in oak, elm, cottonwood, sycamore and alder. In structures, infestations resemble those of carpenter ants but the excavated material has a finer texture. To build nest chambers, which are composed of a paper-like material, the ants mix a combination of plant and soil materials that are cemented together by a substance produced by the ants. Brood chambers are maintained inside the matrix. These ants often congregate in hollows in building insulation or wood forming temporary resting places for foragers. Attempts to locate nests often fail as they are temporary and a vacated as the forager move to new food sources. Velvety tree ants are aggressive and attack and spray intruders with an odor that resembles that of the odorous house ant. These ants are predatory, scavengers and are also attracted to honeydew produce by aphids and other insects.

Exotic Ants of Interest

Army Ants

The most spectacular and well-known ants are the legionary, or army ants of the humid tropical forests. These ants do not construct nests, but form temporary clusters called bivouacs in the shelter of fallen trees or other partially exposed locations. The workers form a solid mass up to a yard wide, which consists of layer after layer of individuals hooked together by their tarsal claws. The queen, larvae, pupae, and eggs are located in the center of this mass.

File:Safari ants tunnel.jpg
Army ants, not as dangerous to humans as commonly believed. Courtesy of Mehmet Karatay CC BY-SA.3.0

The night is passed in a tight cluster, but at the first sign of light the cluster dissipates and hoards of workers fan out from the bivouac in all directions. Soon, one or more columns form and begin to search for food. The workers lay down a pheromone trail for others to follow while the soldiers guard the perimeter of the trail. Workers establish numerous columns that change positions behind the advancing hoards of ants—flushing out large numbers of prey (arthropods, small reptiles and rodents). The prey is stung, killed and transported to the rear as food for the larvae. At the end of the day the cluster is reformed. When the food supply is depleted around the area of the bivouac, the colony relocates.

Some colonies of army ants may number as high as one million individuals. Because of the spectacular size of their colonies and ‘raiding’ nature of these insects, they have been used repeatedly by the motion picture industry. Actually, army ants pose no threat to humans or other large animals.

The authors recently had the opportunity to observe army ant behavior in Costa Rica. One morning we were walking down a dirt road with several students collecting insects. Collecting was not that good but suddenly hoards of insects, spiders and even a few scorpions and lizards started pouring out from the underbrush across the road. After a few moments of excellent collecting, we decided to investigate the reason for this windfall. And, as you might suspect, there was a column of army ants moving through a gully to the side of the road. Of course all the animals in its path were attempting to flee. On the following evening, a column of army ants raided the students' cabin. The students were not awakened, but the following morning they were very disappointed to see that the army ants had stolen most of the several thousand insects they had collected and mounted on pins over the past week. Shortly thereafter, I decided to test the reports that army ants pose no threat to humans. There was a column moving through our pension grounds--so I placed my foot directly in their path. They merely ignored this obstacle and marched over and around it.

While the army ants are primarily found in the New World tropics, the driver ants are found in the tropics of Africa. Both types are very similar as far as their behavior and biology is concerned. One distinct difference is that while large colonies of army ants may number one million, colonies of driver ants can reach 200 million. With such huge numbers, they present more of a threat to humans and other animals. There have been human deaths recorded from the raids of these critters (mostly infants). In these cases, death has typically occurred from suffocation as a result of the ants entering and filling the lungs. 

The mating behavior of these ants is especially strange. The males are drawn to the foraging columns supposedly looking for a mate. Instead of finding a queen, the sterile workers quickly swarm the males and immediately tear their wings off. Then they carry them off and basically imprison them until a potential new queen is available.

Bullet Ants

This ant is primarily found in rain forests ranging from Nicaragua to Paraguay and Australia. This huge (1 inch) beast is called the bullet ant because its sting feels like being shot by a bullet. On the Schmidt Sting Index of Pain, bullet ants rate as the number one most painful sting found in the arthropods. When defending their nests, they swarm out, release a strong odor and stridulate, an audible sound (said to sound like a shriek) and then grab and impale their intruder. In Central-South America they are referred to as the 24-hour ant, referring to the pain described as “of burning, throbbing, all consuming pain” that may last a day or more.

Image: a 1-inch Costa Rican bullet ant. Image Dr. Kaae

As with many other arthropods, bullet ants play a ceremonial role in some tribes of the rain forests. The Satere-Mawe people of Brazil use this ant in the right of passage of boys into manhood. In this case, live bullet ants are woven into a sleeve made of leaves with the stingers of living ants pointing inward. Once the sleeve is place on the arm, the goal is to leave it on for 10 minutes without crying due to the stings. When finished, the boy’s arms are temporarily paralyzed and they may shake uncontrollably for days. To fully complete the initiation, however, the boys must go through this ordeal a total of 20 times over a several month’s period or years.

Trap Jawed Ant (Fastest of All Animals)

A species of ant native to Central and South America has been recorded as the fasting moving animal part, with biologists clocking the speed at which this species of ant closes its mandibles at 35 to 64 meters per second. Based on relative size, this equates to 78 to 145 miles per hour and according this is reported as the fastest self-powered predatory strike in the animal kingdom. The average duration of the strike of this ant closing its mandible equates to 2,300 times faster than the blink of an eye. Their jaws are used to capture prey and to defend its self. The acceleration is huge relative to the tiny mass of the mandibles. The closing of its jaws are functioning in the outer known limits in biology in terms of speed of closure and acceleration. These ants possess a latch system which is essential in obtaining these explosive speeds. Muscles alone are incapable of producing such fast movement. For example, if an individual throws an arrow, it wouldn't travel very far. But on the other hand, with a crossbow, elastic energy is stored in the bent bow, and when the trigger (latch) is released, the stored energy is unleashed in an instant and the arrow shoots out very fast and goes a much greater distance. That is precisely what really fast organisms utilized to reach these great speeds. In comparison, animals such as trap-jaw ants and mantis shrimp (previously held the record for swiftest strike) utilize energy stored within their own bodies. The mandibles of this ant are held cocked by a pair of huge, opposing muscles in its head. The muscles are sprung when their latches, each are triggered.

This speed is not only used to catch prey, but when necessary, the trap jawed ant can launch itself into the air with a mere snap of its jaws, achieving heights that roughly translates (compared to 5-foot-6-inch human) into a height of 44 feet and a horizontal distance of 132 feet. The trajectory of the jump is dependent on the purpose of the strike. When the ant approaches and strikes a large intruder or predator with its jaws, it is simultaneously catapulted away from the aggressor, perhaps leaving behind a crippled victim in the process. In comparison, when the ant needs to escape quickly from an intruder, it strikes its jaws against the ground and flings itself into the air. In these "escape jumps," the ant is jettisoned to heights of 6.1 to 8.3 centimeters, but just 3.1 centimeters horizontally.

Honey Ants

Ants vary tremendously as to their food preferences, size and colony locations. The honey ants are among some of the more interesting species. Normally, they live in arid desert regions of the world; their primary diet is honeydew, which they collect from aphids and other Homoptera. In such dry areas, honeydew-producing insects are common during the rainy season, only when host plants prevail. Since in most of these areas this season only lasts a few months, honey ants have developed a means of storing honeydew from season to season. A special form of worker called the replete, or reservoir ant, accomplishes this. These repletes are fed huge amounts of honeydew; consequently, their abdomens stretch to many times the normal size, sometimes the size of a  grape. Once fed, reservoir ants remain inactive and store honeydew for many months. In many areas of the world, reservoir honey ants are human’s food; they are collected and their abdomens are bitten off. The stored honeydew gives them a candy-like taste.
Worker media and replete castes of honey ants. Image courtesy Greg Hume en Wikepedia CC BY-SA 2.5

Worldwide there are a half dozen or so kinds of ants that exhibit excessive repletism; all of which are properly called honey ants.

A honey ant colony normally contains a single fertile queen and thousands of sterile female workers. The sole function of queen is egg production, while the workers are responsible for colony labor. Honey pot ant workers are polymorphic-they come in different sizes, ranging 10-fold or more in body weight. This difference in size and shape allows for more effective task specialization. As an example, the smallest workers or minims tend to remain in the nest and function as nursemaids,thus tending the queen, caring for the developing immatures (eggs, pupae, larvae) and the essential repletes. Medium or larger size works typically forage for food, excavate the nest and defend the colony defense. The largest workers or majors are most likely to develop into repletes. Honey ant societies may also contain numerous non-working reproductive forms, or winged males and virgin queens. Winged forms, called alates, are produced when colony populations reach an optimal size and become reproductively mature. Then, a portion of the brood raised each year is converted into individuals designed to mate, disperse and start new colonies. Mating flights typically are nocturnal or crepuscular and generally occur only once a year following the first heavy precipitation of the summer rainy season.

The reproductive forms pour out of the nest and swarm into the air, mating on the fly. Young queens take only 1 mating flight; they store viable sperm long-term in a special organ, called a spermatheca, which is then used for fertilizing eggs throughout the remainder of their lives.

The males, their primary function completed, die shortly after mating. The inseminated queens drop to the ground, twist off their now useless wings, and scamper across the surface of the warm wet ground, looking for a place to burrow. The vast majority of the queens fall victim to a barrage of predators including birds, lizards, spiders and especially, other ants. Surviving queens must be well below ground before the rising sun relentlessly dries and bakes the surface. The queens seal themselves inside humid, subterranean cavities and do not forage; rather, they rear their first brood of tiny workers, called nanitics, relying solely on their stored fat reserves and metabolized flight muscles. Colony growth is slow at first, but soon rapidly accelerates as additional ants are added to the worker force.