Vertebrate Pests Part 1


4 Credits
Category: 2, 7D, 8


Identification. Basically, voles look like mice. They are rodents like mice with a few differences: voles have short hairy tails and stouter bodies. Their heads are somewhat rounder and their eyes and ears are rather small in comparison to mice. There are approximately 23 species of voles in the United States. They are sometimes known as meadow mice or field mice in North America. Of the many species of meadow mice found in the United States, only Microtus californicus and Microtus montanus are economically important in the west.  M. californicus has by far the widest distribution and therefore causes the most damage in both agricultural and urban situations. The biology and control of all species are quite similar.

A typical vole or meadow mouse. Image Courtesy Soebe, edited by Fashionslide CC BY-SA 3.0

 Moles, mice, gophers, rats and even shrews have similar characteristics and behavioral tendencies. Voles can perplex applicators by reoccupying old abandoned mole tunnels rather often, thus confusing the applicator into thinking that moles are active. They live quite well by feeding on small plants. Like shrews they will eat dead animals and, like mice or rats, they can live on just about any nut or fruit. Additionally, voles will target plants more than most other small animals.  Voles will readily "girdle" or eat the bark of small trees and ground cover much like a porcupine. This girdling will readily kill young plants and can weaken other for trees or shrubs. Voles readily consume root systems and will burrow under plants or ground cover to resulting in death of the plants. Bulbs are commonly attacked by voles. They eat a wide variety of plants, but most frequently attack forbes and grasses. In late summer and fall, they store seeds, rhizomes bulbs, and seeds. In the fall and winter they are readily draws to bark of trees which they readily consume. Occasional food items include insects, snails and animal remains.

General Biology. Voles are active day and night, all year-round. They do not hibernate as with some other rodents such as ground squirrels. Their home range is usually 1/4 acre or less but can vary with population density, season, habitat, food supply, and other factors. Voles are semi-fossorial (meaning that they dig below ground but do not stay below ground constantly) and construct many tunnels and surface runways with numerous burrow entrances. Their relatively short single burrow system may contain several adults and young.

Voles may breed throughout the year, but most commonly in spring and summer. In the field, they have 1 to 5 liters per year; however, they have produced up to 17 liters per year in a laboratory. Litter sizes range from 1 to 11, but usually average 3 to 6. The gestation period is about 21 days. Young are weaned by the time they are 21 days old and females mature in 35 to 40 days. Life spans are short, probably ranging from 2 to 16 months. In one population, there was 88% mortality during the first month of life.

Population levels of these animals are very cyclic and may peak every 2 to 5 years; however, this is not considered predictable. Occasionally under ideal conditions when populations explode, extremely high vole densities are reached. Dispersal, food quality, climate, predation, physiological stress, and genetics have been shown to influence population levels. Other factors probably also play a part.  Very high densities may be reached during population irruptions. Reportedly in given area vole densities ranged considerably from 200 to 500 per acre and may have reached 4,000 per acre. Being so common they are important prey for a number of vertebrates including snakes, coyotes, owls hawks, and weasels to name a few,; however, predators do not normally control vole populations, mainly because their high seasonal populations.

Damage. Because their ability to girdle seedlings as well as mature trees they have the ability to cause excessive damage to various plants including ornamentals, orchards, and tree plantings. This type of activity typically occurs in fall and winter. Field crops (for example, alfalfa, grain, clover, sugar beets and potatoes) may be damaged or completely destroyed by these pests.  Their extensive runway and tunnel activity interferes with irrigation and can causing levee banks and checks to wash out. Their burrowing may ruin golf courses, lawns and other types of ground covers.

Girdling and gnawing are not necessarily indicative of the feeding activity of voles, since other animals, such as squirrels and rabbits, may cause similar damage. Vole girdling appears different from that of other animals by the non-uniform appearing gnaw marks. In addition they appear at various angles and in irregular patches. These marks are approximately 1/8 inch wide and  3/8 inch long. Rabbit gnaw marks are larger and not distinct. Rabbits also cleanly clip branches and twigs with clean cuts. Identification of mole feeding can be enhanced by their feces, tracks, and burrow systems.

The most readily identifiable symptom of the presence of moles is their shallow surface winding 1 to 2 inch wide runways leading through vegetation. These typically lead to 2 or more openings and are typically clutter with mole feces and pieces of stems, leaves and other o vegetation. The relative short runways lead to underground burrows that consist of short branching tunnels, food storage areas and nests.

These mice do not pose any major public health hazard due to their rare contact with humans: however, as with other rodents, they may carry disease causing organisms, such as those that cause plague and tularemia. Protective clothing should be worn when treating in area where these disease causing organism are known to occur.

Legal Status. Voles are classified as nongame mammals and can be controlled when causing damage. Contact your local state wildlife agency for details regarding applicable codes and regulations.

Control. Quarter inch mess hardware cloth cylinders made of hardware cloth may be used to exclude voles from seedlings and young trees. The bottom of the cylinder should be buried at least 6 inches in order to prevent the voles from burrowing under the cylinder. The use of large scale fencing is not cost-effective considering the other means of control that are available.

Cultural and habitat modification practices have been used in vole management. Ground cover, weeds and litter in and around cultivated areas can be used to reduce the capacity and attractiveness of these areas to support voles. Lawn and turf should be kept short and frequent mowing is not conducive to mole establishment in these plants. Mulch should be removed to 3 feet or more from the bases of trees. Huge populations of these pests can build up in right-of-ways in ditch banks and canals that are difficult to control. Crop adjacent to these populations can be c protected by controlling vegetation through mowing, spraying, or grazing. Soil tillage can be used to reduce vole damage as it removes harborage, destroys runway and burrow and kills a percentage of these pests. Even though voles are less common in annual crop they do invade and damaging annual crops, especially if harborage cover is available over a long time.  . Frightening techniques are of no use in reducing vole damage.

Chemical control. Repellents utilizing Thiram (also a fungicide) or capsaicin (the “hot” in chilies) as an active ingredient is registered for meadow voles (see Supplies and Materials). These products (or repellents registered for other species) may afford short-term protection, but this has not been demonstrated. Check with your state pesticide regulatory agency for availability.

Zinc phosphide is commonly used for vole control. It is a single-dose toxicant which is formulated as grain baits and or pellets. These baits typically are hand broadcast at rates of 6 to 10 pounds per acre or are placed in the shallow runways and burrow openings. In this the pellets are the easiest formulation to use as they can be easily distributed.  Although prebaiting is not generally needed or recommended to achieve adequate control, it may be needed when a population of these pests has been treated several times resulting in bait shyness. These baits are potentially hazardous to birds, especially waterfowl. Placing bait into the open burrows may reduce this hazard.

Anticoagulant baits (diphacine or cholophacinone) have been used in controlling voles. They are slow-acting and require from five to fifteen days to be effective. Multiple feedings over a several day period are needed for most anticoagulants must occur daily to gain control. In addition to broadcasting and hand placement of these bait, they can also can be placed in bait stations. Anticoagulant baits can be glued to the inside surface of a water proof tube. Tube size is about 5 inches long by 1 1/2 inches in diameter. Bait containers are essential to protect the bait from moisture and limit the possibility of non-target animals and children from consuming bait.

Fumigants usually are not recommend for control of these pests as the burrow are shallow allowing escape of the toxicant from the soils and due to the fact that there are multiple openings of the burrows.

Deer Mice-Peromyscus spp.

Left. Adult Deer Mouse. Right. White Footed Mouse.  Images Courtesy of 6th Happiness 6th Happiness. CC BY-SA 3.0

Identification. The scientific name of deer mouse is Peromyscus maniculatus. The species has 66 subspecies, all of which are tiny mammals that are plentiful in number. The deer mouse is described as a small rodent that lives in the Americas and is closely related to the white-footed mouse, Peromyscus leucopus.  Because the two species are extremely similar in appearance, they are best distinguished through red blood cell agglutination tests or karyotype techniques. The deer mouse can also be distinguished physically by its long and multicolored tail. Deer mice are small, only 3 to 4 inches long not including the tail. They have large beady eyes and large ears giving them good sight and hearing. Their soft fur can vary in color from white to black, but all deer mice have a distinguishable white underside and white feet.

Biology. Deer mice are nocturnal creatures who spend the day time in areas such as trees or burrows where they have nests made of plant material. The pups within litters are kept by the mother within an individual home range. Deer mice do not mingle in groups with their litters. During their development stages, the mice within one litter interact much more than mice of 2 different litters. Although deer mice live in individual home ranges, these ranges tend to overlap. When overlapping occurs, it is more likely to be with opposite sexes rather than with the same sex. Deer mice that live within overlapping home ranges tend to recognize one another and interact a lot.

This species can reproduce throughout the year, though in most parts of their range they breed from March to October. Deer mouse breeding tends to be determined more by food availability rather than by season. In Plumas County, California deer mice bred through December under good environmental conditions but ceased breeding in June of years. They breed throughout the year in the Willamette Valley, but in other areas on the Oregon coast there is usually a lull during the wettest and coldest weather.  In southeastern Arizona at least one-third of captured deer mice were in breeding condition in winter. In Virginia breeding peaks occur from April to June and from September to October.

Female deer mice construct nests using a variety of materials including grasses, roots, mosses, wool, thistledown, and various artificial fibers. The male deer mice aid the female in raiaing the litter and keep them together and warm for survival.

In a study, less than half of both male and female deer mice left their original home range to reproduce. This means that there is intra-familial mating and that the gene flow among deer mice as a whole is limited.

Deer mice reproduce profusely and are highest in numbers among their species compared to other local mammals. Peromyscus species gestation periods range from 22 to 26 days. Typical litters are composed of 3 to 5 young, although litter size ranges from1 to 9 young. Most females have more than 1 litter per year. Three or 4 litters is probably typical; however, in captivity they havew produced as many as 14 litters in one year. Males usually live with the family and help care for the young.

Deer mice pups are born blind, naked and helpless; development is rapid. Young deer mice have full coats by the end of the second week; their eyes open between 13 and 19 days and they are fully furred and independent in only a few weeks. Females lactate for 27 to 34 days after giving birth; most young are weaned at about 18 to 24 days. The young reach adult size at about 6 weeks and continue to gain weight slowly thereafter.

Age of first estrus averages about 48 days; the earliest recorded was 23 days. The youngest wild female to produce a litter was 55 days old; it was estimated that conception had occurred when she was about 32 days old

Deer mouse pups usually disperse after weaning and before the birth of the next litter, when they are reaching sexual maturity. Occasionally juveniles remain in the natal area, particularly when breeding space is limited. Most deer mice travel less than 500 feet (152 m) from the natal area to establish their own home range. Their maximum life span is 96 months: the mean life expectancy is 45.5 months for females and 47.5 for males. In many areas deer mice live less than 1 year. One captive male deer mouse reportedly lived 32 months, and there is a report of a forest deer mouse that lived 8 years in captivity (another mouse was fertile until almost 6 years of age).

The majority of deer mice nest is up high in large hollow trees. They nest alone for the most part but will sometimes nest with a deer mouse of the opposite sex. They are populous in the western mountains and live in wooded areas and areas that were previously wooded. The deer mouse is generally a nocturnal creature. Deer mice can be found active on top of snow or beneath logs during the winter seasons.

They inhabit a wide variety of plant communities including grasslands, brushy areas, woodlands, and forests. In a survey of small mammals on 29 sites in subalpine forests in Colorado and Wyoming, the deer mouse had the highest frequency of occurrence; however, it was not always the most abundant small mammals.  Deer mice were trapped in four of six forest communities in eastern Washington and northern Idaho, and they were the only rodent in Ponderosa pine savanna. In northern New England deer mice are present in both coniferous and forests. Deer mice are often the only Peromyscus species in northern boreal forest Subspecies differ in their use of plant communities and vegetation structures. There are 2 main groups of deer mouse: the prairie deer mouse and the woodland or forest deer mouse group.

This species is often active in open habitat; most subspecies do not develop hidden runways the way many voles do. Within open habitat in forests deer mice have a tendency to visit the nearest timber. In central Ontario deer mice used downed wood for runways. They nest in burrows dug in the ground or construct nests in raised areas such as brush piles, logs, rocks, stumps, under bark, and in hollows in trees. Nests are also constructed in various structures and artifacts including old boards and abandoned vehicles. Nests have been found up to 79 feet (24 m) above the ground in Douglas-fir trees.

Deer mice are important prey for snakes, owls, mink, marten, skunks, bobcat, domestic cat, foxes, and ringtail.

They are omnivorous; the main dietary items usually include seeds, fruits, arthropods, leaves, and fungi; fungi has the least amount of intake. Throughout the year, the deer mouse will change its eating habits to reflect on what is available to eat during that season. During winter months, the arthropods compose of one-fifth of the deer mouse's food. These include spiders, caterpillars, and heteropterans. During the spring months, seeds become available to eat, along with insects, which are consumed in large quantities. Leaves are also found in the stomachs of deer mice in the spring seasons. During summer months, the mouse consumes seeds and fruits. During the fall season, the deer mice will slowly change its eating habits to resemble the winter's diet.

Control. Physically excluding an offending animal from the area being damaged or disturbed is often the best and most permanent way to control the problem. Depending upon size of the area to be protected, this control method can range from inexpensive to prohibitively costly.

For example, damage by birds or rabbits to ornamental shrubs or garden plants can be reduced inexpensively by placing bird netting over the plants to keep the pests away. On the other hand, fencing out deer from a lawn or garden can be more costly. Materials needed for exclusion will depend upon the species causing the problem. Large mammals can be excluded with woven wire fences, poly-tape fences, and electric fences; but many communities forbid the use of electric fencing in their jurisdictions. Small mammals and some birds can be excluded with netting, tarp, hardware cloth or any other suitable material; nets come in different weave sizes suitable for different animals to be excluded.

However, exclusion can interfere with the natural movement of wildlife, particularly when exclusion covers large areas of land.

Modifying an animal’s habitat often provides lasting and cost-effective relief from damage caused by nuisance wildlife. Habitat modification is effective because it limits access to one or more of the requirements for life – food, water or shelter. However, habitat modification, while limiting nuisance wildlife, may also limit desirable species such as songbirds as well.

Rodent- or bat-proofing buildings by sealing cracks and holes prevent these animals from gaining access to suitable habitats where they are not welcome. Storing seed and pet food in tightly closed containers, controlling weeds and garden debris around homes and buildings, and storing firewood and building supplies on racks or pallets above ground level are also practices that can limit or remove the animals’ sources of food, water or shelter.

Using a repellent that changes the behavior of an animal may lead to a reduction or elimination of damage. Several available repellents, such as objectionable-tasting coatings or odor repellents, may deter wildlife from feeding on plants. Other repellents such as sticky, tacky substances placed on or near windows, trees or buildings may deter many birds and small mammals. Unfortunately, most wildlife soon discover that repellents are not actually harmful, and the animals may quickly become accustomed to the smell, taste or feel of these deterrents.

Chemical repellents applied outdoors will have to be reapplied due to rain or heavy dew, or applied often to new plant growth to be effective. Failure to carefully follow the directions included with repellents can drastically diminish the effectiveness of the product. Some repellents contain toxic chemicals, such as paradichlorobenzene, and are ineffective unless used at hazardous concentrations. Other more natural repellents contain chili pepper or capsaicin extracted from hot peppers.

However, even under the best of conditions, repellents frequently fail to live up to user expectations. The reason for this is twofold. First, many repellents simply don't work. For example, peer-reviewed publications have consistently shown that ultrasonic devices do not drive unwanted animals away. Second, even when the repellent has been shown to work, animals in dire need of food will "hold their nose" and eat anyway because the alternative is essentially death by starvation. Repellents are most successful (referring to products actually demonstrated by peer-reviewed research to be effective) when animals have access to alternative food sources in a different location.

Glue traps and boards can be either a lethal or non-lethal method of control. Glue boards can be used to trap small mammals and snakes. Applying vegetable oil will dissolve the glue, allowing for release, but caution must be taken to avoid scratches and bites from the trapped animal.

Using traps can be very effective in reducing population of certain species. However, many species cannot be trapped without a permit. In most cases, homeowners may trap an offending animal within 100 yards of their residence without a permit, however relocation is often illegal.

Traditional live traps such as cage or box traps are easily purchased at most garden centers or hardware stores. These traps allow for safe release of the trapped animal. The release of the animal to another area may be prohibited by state law, or may be regulated by the local Department of Fish and Game. Leghold traps may allow for either release or euthanasia of the trapped animal. Traps such as body-gripping traps, scissor and harpoon traps, as well as rat/mouse snap traps, are nearly always lethal. Knowledge of animal behavior, trapping techniques, and baits is essential for a successful trapping program.

Frightening devices such as bells, whistles, horns, clappers, sonic emitters, audio tapes and other such devices may be quite successful in the short term for repelling an animal from an area. Other objects such as lights, reflectors and windmills rely on visual stimulation to scare a problem animal away. Often nuisance animals become accustomed to these tactics, and will return later if exposed to these devices daily.

Zinc phosphide is commonly used for vole control. It is a single-dose toxicant which is formulated as grain baits and or pellets. These baits typically are hand broadcast at rates of 6 to 10 pounds per acre or are placed in the shallow runways and burrow openings. The pellets are the easiest formulation to use as they can be easily distributed.  Although prebaiting is not generally needed or recommended to achieve adequate control, it may be needed when a population of these pests has been treated several times resulting in bait shyness. These baits are potentially hazardous to birds, especially waterfowl. Placing bait into the open burrows may reduce this hazard.

Anticoagulant baits (diphacine or cholophacinone) have been used in controlling these pests. They are slow-acting and require from 5 to 15 days to be effective. Multiple feedings over a several day period are needed for most anticoagulants to gain control. In addition to broadcasting and hand placement of these baits, they can also can be placed in bait stations. Anticoagulant baits can be glued to the inside surfaces of a water proof tube. Tube size is about 5 inches long by 1 1/2 inches in diameter. Bait containers are essential to protect the bait from moisture and limit the possibility of non-target animals and children exposure.

Hantavirus and Deer Mice.  Because these mice are known reservoir of this virus, contact with deer mice is potentially very dangerous. This virus is spread when mouse urine, droppings and or carcasses are handled or otherwise disturbed. In such situations, the virus can become airborne resulting in possible inhalations by individuals in the area.  These droppings and other waste products are mainly located in mouse runways near drawers and cupboards, and other food storage areas. The fecal pellets are smooth and pointed at the ends. They measure between 1/8 to1/4 inches in length. Over 6 months a single pair of adult mice can consume 6 LBS of food and subsequently produce 18,000 fecal pellets. The removal and disposal of droppings of these mice is instrumental in preventing the spread of diseases associated with these mice. Of tantamount importance, great care must be used in handling mouse droppings. The use of face masks, such as surgical masks, and gloves are highly recommended in doing so. It is highly advisable that the carcasses, droppings, and  adjacent areas are sprayed with disinfectants prior to sweeping. Vacuuming should not be used in removal of the bye-products because this may increase the release of Hantavirus into the air.

Symptoms of this disease is similar to those that are typical of flu. The disease has been around for quite a while and it is likely that a number of individuals in the U.S. have been infected in the past, but it was not recognized as the hantavirus until 1993. At that time, there was an outbreak of this fatal respiratory disease on an Indian reservation at the border of Colorado, Utah, and New Mexico. Since then the disease has been reported in every western state, as well as many eastern states. As previously noted rodents, especially deer mice, are reservoir animals. The virus mainly occurs in their feces and urine, but there are no symptoms of its presence. Humans are possibly infected when exposed to contaminated dust from mice nests or droppings. The disease is not spread from human to human. One of the common sources of contacting this dust occurs when cleaning long-empty sheds, homes, or other enclosed areas

In the United States, as of July 2010, 8 states had reported 30 or more cases of hantavirus since 1993- Mexico (84), Colorado (70), Arizona (62), California (42), Washington (41), Texas (37), Utah (31) and Montana (30). Other states reporting a significant number of cases include Idaho (16), Kansas (15), South Dakota (15), North Dakota (12) and Oregon (11).

In late August and early September of 2012, 8 new cases of hantavirus were confirmed, including 4 deaths, in the Curry Village area of Yosemite National Park. On Long Island, David Hart Stein, a chiropractor, died in June 2011, after contracting hantavirus. His story is featured in the HBO documentary Hard Times, Lost on Long Island.

In addition to infecting rodents, hantaviruses are known to be carried by shrews and moles. In Mexico a number of rodents have been found to carry hantaviruses: Megadontomys thomasi, Neotoma picta, Peromyscus beatae, Reithrodontomys megalotis and Reithrodontomys sumichrasti.

In Canada, there was one confirmed death in Northern British Columbia in January, 2013 and at least one confirmed death in Kindersley, Saskatchewan, in June 2013. Another death in the Kindersley area (June 2013) may also be linked to hantavirus. One confirmed case (July 2013) in Burr, Saskatchewan (near Kindersley); the patient was gravely ill but survived.

Lyme Disease. Lyme disease (Lyme borreliosis) is an infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in North America, whereas Borrelia afzelii and Borrelia garinii cause most European cases. The first known existence of the Borrelia bacteria dates back to up to 20 million years ago. The disease is named after the towns of Lyme and Old Lyme, Connecticut, US, where a number of cases were identified in 1975. Although it was known that Lyme disease was a a tick-borne disease as far back as 1978, the cause of the disease remained a mystery until 1981, when B. burgdorferi was identified by entomologist Dr.Willy Burgdorfer.

Lyme disease is the most common tick-borne disease in the Northern Hemisphere. Borrelia is transmitted to humans by the bite of infected ticks belonging to a few species of the genus Ixodes ("hard ticks"). Early symptoms may include fever, headache, and fatigue. A rash occurs in 70–80% of infected persons at the site of the tick bite after a delay of 3–30 days (average is about 7 days), and may or may not appear as the well-publicized bull's-eye (erythema migrans). The rash is only rarely painful or itchy, although it may be warm to the touch. About 20–30% of infected persons do not experience a rash. Left untreated, later symptoms may involve the joints, heart, and central nervous system. In most cases, the infection and its symptoms are eliminated by antibiotics, especially if the illness is treated early. Delayed or inadequate treatment can lead to more serious symptoms, which can be disabling and difficult to treat. The term "chronic Lyme disease" is controversial and not recognized in the medical literature, and most medical authorities advise against long-term antibiotic treatment for "chronic Lyme disease".

This "classic" bull's-eye appearance is also called erythema migrans. A rash caused by Lyme does not always look like this. Around 20% to 30% of persons who are infected with Lyme disease may have no rash at all. Image Courtesy CDC. Public Domain

Lyme disease can affect multiple body systems and produce a range of symptoms. Not all patients with Lyme disease will have all symptoms, and many of the symptoms are not specific to Lyme disease, but can occur with other diseases, as well. The incubation period from infection to the onset of symptoms is usually one to two weeks, but can be much shorter (days), or much longer (months to years).

Symptoms most often occur from May to September, because the nymphal stage of the tick is responsible for most cases. Asymptomatic infection exists, but occurs in less than 7% of infected individuals in the United States. Asymptomatic infection may be much more common among those infected in Europe.

Early localized infection. Early localized infection is where the Lyme disease has not yet spread throughout the body. The only area affected is where the infection has first come into contact with the skin. The classic sign of early local infection with Lyme disease is a circular, outwardly expanding rash called erythema chronicum migrans (also erythema migrans or EM), which occurs at the site of the tick bite three to 30 days after the tick bite. The rash is red, and may be warm, but is generally painless. Classically, the innermost portion remains dark red and becomes thicker and firmer); the outer edge remains red; and the portion in between clears, giving the appearance of a bull's eye. However, partial clearing is uncommon, and the bull's-eye pattern more often involves central redness.

The EM rash associated with early infection is found in about 80% of patients and can have a range of appearances including the classic target bull's-eye lesion and nontarget appearing lesions. The 20% without the EM and the nontarget lesions can often cause misidentification of Lyme disease. Patients can also experience flu-like symptoms, such as headache, muscle soreness, fever, and malaise. Lyme disease can progress to later stages even in patients who do not develop a rash.

Early disseminated infection. Within days to weeks after the onset of local infection, the Borrelia bacteria may begin to spread through the bloodstream. EM may develop at sites across the body that bear no relation to the original tick bite. Another skin condition, apparently absent in North American patients, but occurs in Europe, is borrelial lymphocytoma, a purplish lump that develops on the ear lobe, nipple, or scrotum. Other discrete symptoms include migrating pain in muscles, joints, and tendons, and dizziness and heart palpitations from conduction irregularities such as third-degree heart block.

Various acute neurological problems, termed neuroborreliosis, appear in 10–15% of untreated patients. These include facial palsy, which is the loss of muscle tone on one or both sides of the face, as well as meningitis, which involves severe headaches, neck stiffness, and sensitivity to light. Radiculoneuritis causes shooting pains that may interfere with sleep, as well as abnormal skin sensations. Mild encephalitis may lead t memory loss, sleep disturbances , or mood changes. In addition, some case reports have described altered mental status as the only symptom seen in a few cases of early neuroborreliosis. The disease may also have cardiac manifestations such as atrioventricular block.

Late disseminated infection. After several months, untreated or inadequately treated patients may go on to develop severe and chronic symptoms that affect many parts of the body, including the brain, nerves, eyes, joints, and heart. Many disabling symptoms can occur, including permanent impairment of motor or sensory function of the lower extremities in extreme cases. The associated nerve pain radiating out from the spine is termed Bannwarth syndrome, named after Alfred Bannwarth.

The late disseminated stage is where the infection has fully spread throughout the body. Chronic neurologic symptoms occur in up to 5% of untreated patients. A polyneuropathy that involves shooting pains, numbness, and tingling in the hands or feet may develop. A neurologic syndrome called Lyme encephalopathy is associated with subtle cognitive problems, such as difficulties with concentration and short-term memory. These patients may also experience fatigue. However, other problems, such as depression and fibromyalgia, are no more common in people with Lyme disease than in the general population.

Chronic encephalomyelitis, which may be progressive, can involve cognitive impairment, weakness in the legs, awkward gait, facial palsy, bladder problems,vertigo and back pain. In rare cases, untreated Lyme disease may cause frank psychosis, which has been misdiagnosed as schizophrenia or bipolar disorder. Panic attacks and anxiety can occur; also, delusional behavior may be seen, including somatoform delusions, sometimes accompanied by a depersonalization or derealization syndrome, where the patients begin to feel detached from themselves or from reality.

Lyme arthritis usually affects the knees. In a minority of patients, arthritis can occur in other joints, including the ankles, elbows, wrist, hips, and shoulders. Pain is often mild or moderate, usually with swelling at the involved joint. Baker's cysts may form and rupture. In some cases, joint erosion occurs.

Control.  If left uncontrolled, deer mice can be troublesome and dangerous pests. They are the primary reservoir species of Hantavirus Pulmonary Syndrome, which is extremely harmful to human health. Prevention measures may be taken to ensure that an area does not become host to a deer mouse population. The use of rodent-proofing materials on entryways around the exterior ensures that these rodents cannot enter. Regardless of size, all holes should be sealed with these materials; deer mice possess soft cartilage that allows them to pass through holes less than the size of a dime. Keeping weeds and grass mowed and removing clutter from the yard can make the property less attractive to deer mice.

Defensive packaging of food will also help. Food containers made of stainless steel, glass and thick, heavy plastic are better than paper boxes and plastic bags. Boxes and items stored in garages, attics, or crawlspaces are ideal nesting sites for deer mice. These should be examined carefully. Try to "de-clutter" these areas so that mouse activity will be easier to spot. Removing deer mice from the infested area oftentimes proves difficult. Most methods involve the treatment with traps or toxic baits. Baits should be used with extreme caution according to label directions to avoid harm to children and pets.  Professional pest control treatment may be necessary to treat an existing deer mouse infestation.

Pack Rats, Wood Rats-Neotoma spp

There are many species of wood rats (Neotoma spp.) in United State.  Even though their combined distribution represents a wide area, these rodents rarely cause any significant damage to agriculture or the homeowner.  Normally they do not reach large populations and are typically not found in urbanized or agricultural areas (depending on species), but are found instead in locations such as heavy chaparral, streamside thickets, pine forests, rock slide areas of high elevation forests or desert floors.

Biology. Woodrats reach their greatest diversity in the deserts of the western United States and northern Mexico. Several species are also found in the deciduous forest of the east coast, juniper woodlands in the southwest, oak woodlands along the coastal western United States and in the Sonoran Desert, and in the forest and rocky habitats of the western United States and western Canada.

Each species of pack rat is generally restricted to a given type of habitat within its range. Pack rats live anywhere from low, hot, dry deserts to cold, rocky slopes above timberline. Pack rats build complex houses or dens made of twigs, cactus joints, and other materials. These contain several nest chambers, food caches, and debris piles. Dens are often built in small caves or rocky crevices, but when close by human habitations, woodrats will opportunistically move into the attics and walls of houses. Some Neotoma species, such as the white-throated woodrat (N. albigula), use the bases of prickly pear or cholla cactus as the sites for their homes, using the cactus' spines for protection from predators. Others, like the desert woodrat (N. lepida) will build dens around the base of a yucca or cactus, such as jumping and teddy-bear chollas. The largest species, Neotoma cinerea, has a bushy, almost squirrel-like tail. Bushy-tailed woodrats Neotoma cinerea occupy a range of habitats from boreal woodlands to deserts. They are cliff-dwellers and are often found on isolated, high-elevation exposed boulder areas under a variety of temperature and moisture conditions. They require adequate shelter inside the rocks, though they are occasionally found inhabiting abandoned buildings, as well.

Pack rats are nest builders. They use plant material such as branches, twigs, sticks, and other available debris. Getting into everything from attics to car engines, stealing their ‘treasures’, damaging electrical wiring, and creating general noisy havoc can easily cause them to become a nuisance. A peculiar characteristic is that if they find something they want, they will drop what they are currently carrying, for example a piece of cactus, and "trade" it for the new item. They are particularly fond of shiny objects. These two traits have inspired an anecdote about a man finding his dime replaced by two nickels. They can also be quite vocal and boisterous.

Bushy-tailed woodrats feed primarily on green vegetation, twigs, and shoots. Mexican pack rats eat seeds, fruits, acorns, and cactus.

Adult bushy-tailed woodrat males usually weigh 300-600 g with an average of 405 g, and adult females usually weigh 250-350 g with an average of 270 g. These ranges are relatively large because this species occupies a large geographic range, and its body size is closely correlated with climate. Average males range in size from 310–470 mm with the average being 379 mm and average females range from 272 to 410 mm with the average being 356 mm.

Reproductive habits of rodents are variable in the wild and can become more so when domesticated. Most are born naked and helpless and must be cared for in nests. Some female pack rats have been known to deliver up to five litters per year with each litter having as many as five young. The offspring may open their eyes between 10 to 12 days after being born and are usually weaned between 14 and 42 days. After around 60 days, most become sexually mature.

A pack rat midden is a debris pile constructed by a woodrat. A midden may preserve the materials incorporated into it for up to 50,000 years, thus may be analyzed to reconstruct their original environment, and comparisons between middens allow a record of vegetative and climate change to be built. Examinations and comparisons of pack rat middens have largely supplanted pollen records as a method of study in the regions where they are available.

In the absence of rock crevices or caves, the dens are often built under trees or bushes. The pack rats will also use plant fragments, animal dung, and small rocks in building the den. The vast majority of the materials will be from a radius of several dozen yards of the nest. Woodrats often urinate on the debris piles; sugar and other substances in the urine crystallize as it dries out, creating a material known as amberat, which under some conditions can cement the midden together. The resilience of the middens is aided by three factors. The crystallized urine dramatically slows the decay of the materials in the midden; the dry climate of the American Southwest further slows the decay; and middens protected from the elements under rock overhangs or in caves survive longer.

In cases where damage does occur, much of it is due to the rat’s nest building behaviors.   Neotoma nests are typically cone or dome shaped structures that may be as high and wide as 5 feet and are made out of twigs, rock, bark, manure, tin cans or any other objects that meets the rat’s requirements.  When damage such as stripping of bark or cutting of side braches of citrus or conifers occurs, this is primarily done for nest building purposes.  The name “pack rat” refers to the annoying habit of this rat steals shiny objects and storing them in its nest.  This can be troublesome to the homeowner who starts missing jewelry, coins, watches, silverware and similar objects.


Wood or Pack Rat and Its Nest. Left image Courtesy Forbes USDA.  Right Image courtesy Toiyabe at the English language Wikipedia  CC DY-SA 3.0.  

Assassin bugs are commonly found in wood rat nests and they feed on the rats. In Mexico and South America, but not in the US, these insects vector Chagas disease.  Assassin bugs have a nasty bite and will attack humans, especially if their preferred hosts, the wood rats, are controlled.  In high-risk areas wood rat populations are periodically reduced by sylvatic plague, which presents a potential risk to humans.

Control. Compared to many rat species, wood rats are easily trapped.  This can be accomplished by placing a standard wood based rattrap baited with a prune, nutmeats or raisins near the nest or runways.  Havahart live traps are equally as effective.

The spot treating with zinc phosphide baits has also proven to be effective.   Because the populations of these rats are typically small, broadcast treatment is generally not effective.  Crimped whole oats or oat groats are the preferred grains for baiting.  Scatter a small amount of bait on approximately a one square foot area near the nest or in a runway.  Do this in the late afternoon so ants and other insects do not carry the grain away.  With wood rats, leaving these baits for prolonged periods of time does not improve kill and increases the chance or poisoning non-target animals.  The baits should be removed after 48 hours.

Anticoagulant baits such as chlorophacinone or diaphacinine are effective against wood rats.  Broadcast treatment is inadvisable and these rats frequently fill standard bait stations with sticks and other debris.  As a consequence, open faced bait stations can be used, provided they are covered by inverting a wooden crate or similar object that will allow rats to enter but exclude larger animals.  Normally 4 to 16 ounces of bait are used per station with individual stations placed no more than 100 feet apart. This is all that is necessary considering the limited foraging range of the animals.

Anticoagulant paraffin bait blocks have proven effective in orchard situations.  In this case the blocks can be secured to the limbs of trees where damage has occurred.  These should be removed once control has been attained.  It is extremely important to make sure these blocks are high enough in the trees so dogs and other animas cannot access them.  Dogs readily eat these blocks.

T/F Questions spread throuighout the program. Write down the false answers.Then call in 714-960-8022) or email ( the false answers. Please call inIf you call in please do so 9 to 4  during West Coast hours.

1. A symptom of the presence of voles is “shallow runways” in grass and other vegetation.

2. Meadow mice populations tend to be “cyclic”, reaching peak numbers every 3 or 4 years and then dropping drastically the next year.

3. The main means of controlling large populations of voles is broadcasting zinc phosphide baits at “6 to 10 pounds” per acre or spot treatment with zinc phosphide or anticoagulant baits (the later may not be time efficient).

4.Girdling and gnawing are not necessarily indicative of the feeding activity of voles, since other animals, such as squirrels and rabbits, may cause similar damage. Vole girdling appears different from that of other animals by the non-uniform appearing gnaw marks. In addition they appear at various angles and in irregular patches. 

5 Voles activity is strictly nocturnal and hibernate much like other rodents.year-round. 

6. Deer mouse droppings are primarily seen in mouse runways: “near cupboards”, drawers and other food storage areas.

7. In the span of one month, one pair of deer mice is capable of consuming 4 pounds of food and producing “18,000 fecal pellets”.

8. Normally wood rats do not reach large populations and are typically not found in urbanized or agricultural areas (depending on species), but are found instead in locations such as “heavy chaparral”, streamside thickets, pine forests, rock slide areas of high elevation forests or desert floors.

9. Brodcasrting anti nticoagulant baits  such as chlorophacinone or diphacine are typically effective against wood rats.

Moles have a unique appearance and they are well adapted for their lifestyle. Their shoulders are strong and muscular and their necks are so short that they appear to be almost non-existent. Their heads are wide and their front legs look like and work like a shovel that has been equipped with strong claws that are perfectly adapted for digging. And when moles do dig, it almost appears as they are swimming through the soil. Their forefeet are held close to their heads and are used to push the dirt aside. Their blackish plush fur lies flat when stroked from either direction, and offers little, if any, resistance when a mole moves in either a forward or backward direction through its tunnel. As might be expected, being subterranean critters, they have no use for good vision and their tiny little eyes have fused eyelids. However, they have a good sense of smell and also adapted to detect above ground movements via sensory hairs all over their bodies.

File:Close-up of mole.jpg

Mole. Image Courtesy Michael David Hill. CC BY-SA 3.0

Moles are active year around and throughout the day or night except for the Townsend mole, which is primarily nocturnal. Many develop their own rhythm with some individuals of a species active at night and some during the day. They are almost totally subterranean except for the shrew mole that spends a considerable amount of time above ground foraging for food. As indicated these small creatures feed mainly on worms and insects that they encounter during their burrowing activity; however, most moles eat some plant material during their lives.

These critters are not as prolific as gophers and normally produce one generation of two to six young a year. The young are born in the spring with a gestation period of around one month. The offspring are born relatively large and reach sexual maturity within a few months. It is estimated that the average mole only lives a few years, although this is not well documented due to their secretive way of life.

Moles form two types of tunnels, the most obvious of which are the shallow temporary tunnels where the soil is raised in ridges as the mole searches for food. More permanent tunnels, which can reach a depth of 18 or more inches, are used when the soil dries out, as a nesting location or as a retreat from potential predators. These are typically located near the above ground, cone shaped mounds that are produced as the moles excavate these permanent locations.

As with gophers, moles are solitary although in large populations the Townsend mole occasionally uses common tunnels to access different areas.


Raised ridge that is typical of a mole’s temporary tunneling below ground in search of food. Image Dr. Kaae

Moles are much more difficult to control than gophers. This is due to any of a number of factors. Because they mainly eat worms and insect larvae, there are few, if any, effective commercially available baits. Some pest control operators have claimed to attain some degree of control with a variety of baits with best results occurring when these are placed in the more permanent deeper tunnels.

These vermin do not regularly reuse their temporary tunnels and typically frequent a relatively large area as they move around. Most successful controls are typically aimed at the more permanent tunnels located by deeply probing with a steel rod or gopher probe in the vicinity of the above ground conical shaped mounds. Aluminum phosphide should not be placed in the temporary tunnels as the gas will readily leak from the soil and will not be effective in killing moles in this location. Also dogs have been known to dig up and eat foreign smelling objects such as these. This would result in certain death of the animal. Again, this is not a recommended means of control because this chemical is not registered for mole control.

Elimination of the food source of moles is a preventative means of control. This can be accomplished by using a soil drench insecticide at least once a year in the late summer months. These drenches are mainly aimed at scarab larvae and worms. There are two products which work well for this purpose; Tempo and Bifenthrin Granules. If both are used they will deliver a one-two punch which works well in the long run. The liquid provides a quick knockdown and kills off active larva. Tempo is both easy to use and quick acting. It will last a month or two and its effect is to kill the grubs which moles are seeking. Although the Tempo will provide quick knockdown, the use of Bifenthrin Granules will provide a longer window of protection. This will prove helpful in controlling the larvae which hatch out after liquid treatments. This is important in some climates that have long mild seasons and eggs may be hatching more than one time a year. These granules are easy to apply and will last several months per application. 

Trapping can control moles. However, it is time consuming and relies on knowing which tunnels are currently being used. As a consequence, the individual attempting control may have to return to the general location several times before this can be determined. As previously discussed, moles dig a series of surface runs many of which may not be reused. In order to determine which runs are being used more than once, the applicator may flatten short sections of several runs and return daily to determine if any of those sections have been re-elevated due to the activity of the mole.  Once this has been determined on a few consecutive days, a trap can be set. There are a number of different mole traps but the two most commonly used in California are the Out-of-Sight, the Reddick Harpoon, or the Spear Trap. These traps are either placed directly over (Reddick trap) or around (Out-of-Sight trap) an active tunnel and rely on the mole activating the trap by pushing a trigger located in or directly above the tunnel.

Mole Out O'SightMole Spear Trap

Two common types of mole traps. Left: Out of Sight Trap. Right: Spear Trap.

Some baits are much more effective than others. In fact some are not effective at all and have been taken off the market. Regardless of the type of bait used, one important factor in the baiting of moles is a lot of the bait should be used to insure they find it. Since moles frequently use tunnels only once except for the main den, bait placements made too far apart will be missed. Don't make your placements more than 10 feet apart and try to make the placements as close to the den or main tunnels as possible.

 Another key to mole control is that baiting should be applied after application of chemicals for grub and worm control. Generally speaking, if chemicals are used for control of grubs and worm, baiting should be done at least a day later. This will allow the chemicals to dry and not impact the bait. Spraying over the bait might contaminate it making it unacceptable to moles. On the other hand, if you only bait, expect to have more moles replace the ones you kill. This is due to the fact that you haven't dealt with the food supply. The possible exception to this is Southern California where moles are somewhat rare and replacement is unlikely. On the other hand, in Northern California and Oregon moles are very common pests.

As indicated, there are a number of types of mole bait on the market. An example of one such bait that has a rather unique design is Talpirid Mole Bait. The bait is a rubber worm - very similar to the kind used for fishing. Moles feeding on worms rely on feel for identifying their prey. Talpirid worms are placed in tunnels and burrows which are active and as a mole passes through it will reportedly grab the offering. These worms mimic real earthworms so well that moles won't know the difference. Once found, the worm will be seized and chewed. At that point a lethal dose of bromethalin is ingested causing the mole to die in a day or two.


Taliprid mole bait.  

All things considered, moles are fascinating animals. A 5 ounce mole will consume 45 to 50 lbs. of worms and insects each year. ·Moles can dig surface tunnels at approximately 18 feet an hour. Moles travel through existing tunnels at about 80 feet/minute. Moles contain twice as much blood and hemoglobin as other mammals of similar size. This allows moles to breathe more easily in underground environments with low oxygen.        

Muskrats (Ondatra zibethica)

File:Ondatra zibethicus FWS.jpg

Muskrat. Image courtesy of U.S. Fish and Wildlife Services

Muskrats are found in wetlands, rivers, lakes and ponds and over a wide range of climates and habitats. They are edible and play an important role in nature, as well as a source of food and fur for humans. Some people claim they taste similar to duck or rabbit. They can be found all over North America. In California they range from the Central Valley, Imperial Valley and Colorado River area, northeastern California and scattered along the coast. They have been introduced into South America, Asia and Europe.

Almost half of an adult muskrat is its tail. They are fairly large with a total length of 16 to 24 inches and can weigh from 1.5 pounds up to 4 pounds. They are smaller than beavers and often share their burrows. The weight of an adult muskrat would be approximately four times that of a Norway rat, although they are not much longer than the rat, but they are stockier.

Muskrats are covered with fur that is short and thick and medium dark-brown in color; the belly fur is a bit lighter, but turns partly gray with age. The fur has 2 layers, which helps protect them from the cold water. They have long tails which are covered with scales rather than hair and are flattened vertically to aid in swimming. When they walk on land, the tail drags on the ground, which makes their tracks easy to recognize.

These animals spend a great deal of their life in the water and are well-suited for their semi-aquatic existence, both in and out of water. They can swim under water for an average of 15 minutes. Their bodies, as with seals and whales, are less sensitive to the buildup and presence of carbon dioxide than those of most other mammals. They have the ability to close off their ears to keep out water. Even though their hind feet are partially webbed, their well-developed tail is their main means of aquatic propulsion (swimming).

Muskrats typically inhabit wetlands, areas in or near salt and fresh-water marshlands, rivers, ponds and lakes. Muskrats continue to thrive in most of their native habitat and in areas where they have been introduced. While much wetland habitat has been eliminated due to human activity, a new muskrat habitat has been created by the construction of canals or irrigation channels and resultantly the muskrat remains common and widespread. They are able to live alongside streams which contain the sulfurous water that drains away from coal mines. Fish and frogs perish in such streams, yet muskrats may thrive and occupy these wetlands. Muskrats also benefit from human persecution of some of their predators.

File:Muskrat swimming Ottawa.jpg
Muskrat in natural habitat. Image Courtesy B. Gordon Robertson.

A family typically consists of a male and female pair and their young. Their nests are used for protection of adults and young against the cold weather and potential predators. In the spring, some muskrats do engage in battles with other muskrats over territory or sometimes over choice of mates. In such cases it can be dangerous and some individuals can be seriously harmed or even killed. Muskrats burrow into banks in streams, ponds or lakes where they form an underwater entrance to their nests. Such entrances are six to eight inches wide. In marshes, lodges are constructed from vegetation and mud. Lodges can be as high as three feet. In snowy areas they keep the openings to their lodges closed by plugging them with vegetation which they replace every day. Some muskrat habitats have to be replaced every year as spring floods sometimes sweep away the existing lodges. Muskrats will often build platforms for feeding in wetlands. These critters help maintain open areas in marshes which helps to provide habitat for aquatic birds.

File:Muskrat lodge.jpg

Muskrat nest. Image courtesy of Mongo. Public Domain

Muskrats are most active at night or near dawn and dusk. They feed on cattails and other aquatic vegetation. Young may be born at any time of year, but there are fewer births in winter. The gestation period is 22 to 30 days and two to three litters a year are typical. There are usually five to six young (range of one to 11) per litter which are weaned in about one month.

Although muskrats will eat small animals such as frogs, crawfish, turtles, fish and freshwater mussels, their main diet (about 95%) is made up of plant material. Muskrats follow established trails in swamps and in ponds. After a pond has frozen over, muskrats follow their trails from under the ice. Winter trapping of these critters is based on this behavior.

Muskrat Love. Okay, it was only a song but muskrats, like most rodents, are prolific breeders. A female can produce 2 to 3 litters a year with 5 to 6 young in each litter. At birth, the young are hairless and small (weighing in at about 22 grams). Geography plays a part in how quickly they develop. In southern (warmer) environments, the young mature in about six months while in the northern (colder) environments, the young mature in about 12 months. There does appear to be a dramatic rise and fall pattern to muskrat populations. The muskrat is not alone in this as some other rodents do the same type of population change. Lemmings, for example, do this as well.

Muskrats occasionally can be pests, as they will damage tomatoes, rice, sugar beets and grain, and sorghum. However, they often are blamed for crop damage which is actually caused by resident Norway rat populations in places such as the delta. The major damage caused by muskrats is the weakening or washing out of levees, culverts, and head gates due to their burrowing in earthen banks. In cases where levee soils are peaty or sandy, and where levee or ditch bank walls are thin, it becomes a much more serious problem.     

Legal Status. Muskrats are classified as fur-bearing mammals by the California Fish and Game Code. Muskrats that are injuring growing crops or other property may be removed at any time and in any manner, except that if leg-hold steel-jawed traps are used they shall not have saw-toothed or spiked jaws or have a spread over 4 ¾ inches.

.Control In Rice Fields. Preventive measures include the enlargement of check-banks and development of substantial check boxes thus minimizing their burrowing. A check-bank with a base of 6 feet offers more resistance to erosion due to their burrows than does a narrower bank. Wide banks need wider check boxes as these seem less vulnerable to burrowing by these pests. A recommended box size 2 feet wide, by 18 inches high, and four feet long and should be made of 2 inch lumber. Additional protection is obtained by the use of lateral wings (two feet in length) to discourage muskrats from burrowing along the side of the box.

Muskrats are not difficult to trap, and when their burrows are in narrow banks between rice checks, trapping is simple and effective. Size 1 or 1½ steel traps are preferred and should be chained to a stake in the water so that the critter can swim away from the bank. The weight of the trap pulls the muskrat under the water where it drowns. The trap should be placed at the burrow entrance just beneath the surface of the water where the muskrat can swim into it easily. It is not necessary to remove human scent from the traps and no bait is needed. Another effective muskrat trap is the Conifer trap, size 110, which kills the animal almost immediately.

Control in Irrigation Canals.  Frequently muskrats make burrows about junctions of canals, especially when there is a wooden or cement structure damming the water. Such burrows may lead from one canal to another, often beneath the protection of the structure. Differences in water level cause burrows to erode rapidly and those covered by the cement structure of the head gate are difficult to destroy or fill.

Head gate foundation should be constructed to prevent muskrat burrowing. This may be accomplished by extending a concrete apron 15 feet in both directions from the head gate and along the sides and bottom of the canal. Use of wire netting on canal banks about head gates and other especially vulnerable trouble spots will prevent digging. Two inch diamond mesh (No. 14 gauge, galvanized after weaving) placed 2 feet above and 2 feet below the water should be used.

Traps should be located in the burrow and covered by an inch or 2 of water, and chained to a stake placed in the deeper water. Once trapped, the burrow should be caved in and the entrance blocked. If there is danger of water flooding the burrow and subsequently flowing through the bank, dirt should be piled in front of the entrance to hold back the water until the animal is trapped.

True/False Questions. 

10. Moles have a good sense of smell, but can readily detect any above “ground movements” with sensory hairs that are spread throughout the body.

11. Mole mounds are typically “cone shaped” while the larger gopher mounds typically are horseshoe shaped.

12. Moles typically have poor eyesight.

13.  Most mole species mainly feed on worms and insects found in the soil. As a consequence, they do not damage many plants but causes damage due to their unsightly mounds and raised tunnels.

14.  Moles typically dig 2 types of tunnels, the more obvious of which is the shallow temporary tunnels that result in raised ridges at ground level. These type tunnels are not frequently reused.

15. Elimination of the mole’s food source by applying soil “drench pesticides” can result in a degree of control.

16. Some baits are much more effective for mole control than others. In fact some are not effective at all and have been taken off the market. Regardless of the type of bait used, one important factor in the baiting of moles is a lot of the bait should be used to insure they find it. 

17. Muskrate an chiefly active during dayligh hours.

18. Muskrat fur has 2 layers, which helps protect them from the “cold water”.

19. Muskrats continue to thrive in most of their native habitat and in areas where they have been introduced. While much wetland habitat has been eliminated due to human activity, a new muskrat habitat has been created by the construction of canals or irrigation channels and as a result the muskrat remains common and widespread.


Striped Skunk (Mephitis mephitis) Western Spotted Skunk (Spilogale gracilis) Eastern spotted skunk (Spilogale putorius)

Skunks are famous for their behavior of squirting a liquid with a strong, foul odor. They vary in appearance depending on species and range in color from brown, black-and-white to cream colored. At one point, they were classified in a subfamily within the family Mustelidae, which includes weasels, ferrets, otters, badgers, and their relatives. However, recent studies indicate that they are classified in a family of their own.

Depending on species, these critters vary in size ranging from 16 to 37 inches in length and weight from one to 18 pounds. They have an elongated body with relatively short, well-muscled legs, and long front claws that are adapted for digging. These critters are typically black and white with some species colored brown or gray, and a few cream-colored. All skunks are striped, even from birth. They may have a thick stripe across back and tail, two slimmer stripes, or a series of white spots and broken stripes (in the case of the spotted skunk). Some also have stripes on their legs.

File:Striped Skunk.jpg
Striped skunks. Image courtesy of Bird Photos. Tomfriediel. en

Skunks are omnivorous, eating both plant and animal material and change their diet as the seasons change. They eat adults and immature insects as well as other arthropods, small and young rodents, salamanders, earthworms, lizards, frogs, snakes, moles, birds, and eggs of various animals. They also commonly consume vegetable matter including roots, berries, leaves, grasses, fungi, and nuts.

In urban areas, these mammals readily consume human garbage. Although less commonly, these pests feed as scavengers consuming rodent and bird carcasses left by cats or other predators or merely road kill. Pet owners, especially those of cats, occasionally encounter a skunk that has entered a garage can or basement where pet food is kept. These pests commonly dig in lawns searching for insect grubs, especially scarab larvae or white grubs and worms.

Skunks are one of the main mammalian predators of the honeybee, relying on their thick fur for protection from the stings of these insects. Skunks scratch at the entrance of a hive and eat the guard bees that function to protect the hive from intruders including skunks. Reportedly, females are known to teach this behavior to their young.       

They are crepuscular (active at dawn) and are solitary when not breeding, though in colder areas they may gather in communal dens in order to conserve warmth. During the day, they remain in burrows which they dig with their powerful front legs and claws or in human-made or natural hollows. Both sexes frequently have overlapping home ranges throughout most of the year; these typically are 3/4 to 11/2 square miles for females and up to 7.7 square miles for males. Skunks, unlike bears and some other mammals, do not hibernate in the winter, but den up for extended periods of time depending on prevailing temperature. In this condition, they remain generally inactive and feed rarely, going through a dormant stage. Skunks often overwinter in a huddle of multiple (as many as 12) females. Males often den alone. With both sexes, the same winter den is often repeatedly used.

Although skunks possess good senses of smell and hearing—both important in a crepuscular omnivore—they have poor vision (not so important). Skunks cannot clearly see (at least well) objects more than about 10 feet away which of course makes them vulnerable to road traffic. In the wild skunks are short-lived with fewer than 10% surviving for longer than 3 years.

Skunks typically mate in early spring and are a polygynous (males typically mate with more than one female). Prior to birth (usually in the spring), females dig a den for their litter of four to seven. At birth skunk kits are deaf, blind, and covered with a soft, thin layer of fur. About three weeks later, their eyes open and they are weaned about two months after birth. The young typically remain with their mother for about one year at which point they are capable of mating. The mother is extremely protective of the young and will readily spray at any sign of danger. The males are not involved in raising the young and may even kill them if given the chance. 

The most well-known feature of skunks is their anal scent glands which they use as a defensive weapon when threatened. They are quite similar in structure but much more developed than glands found in other species of the musk family. Skunks have two glands, one on each side of the anal opening which produce a mixture of sulfur-containing chemicals (referred to as mercaptans), which have an extremely offensive odor that can be described as a combination of garlic, rotten eggs, and burnt rubber. This odor is pungent enough to ward off bears and other possible predators and as it is well-known, can be difficult to remove from clothing, skin, or fur. The fluid from these glands can be sprayed with a high degree of accuracy and as far as seven to 16 feet. The spray can cause irritation of the eyes and skin and even temporary blindness and is sufficiently powerful that it can be detected as far away as up to a mile downwind.

Skunks are reluctant to use this defensive weapon, as they only carry just enough of the chemical for a few uses (about 15 cc) and require 10 or more days to produce another supply. Their bold white and black coloring serves to alert predators of their presence, something that is not forgotten once sprayed. It is advantageous to simply to warn a threatening predator without producing scent. Besides using black and white warning coloration, threatened skunks have a variety of warning behaviors including foot stamping, elaborate routine of hisses, and tail-high threatening postures before resorting to the ultimate defense. For some reasons, skunks usually do not spray other skunks, with the exception of males in the mating season. Though females fight over den space in autumn, they do so without spraying.

Most predatory animals of the Americas, such as badgers, coyotes, wolves, foxes and dogs rarely attack skunks, presumably due to, as a learned or inherited, fear of being sprayed. The one exception is the great horned owl, which is the skunk’s only serious predator. Owls to their advantage have a poor-to-nonexistent sense of smell.

Skunks are commonly found in suburban areas and encounters with dogs and other domestic animals are not uncommon. Many myths exist about the removal of the skunk odor. Unfortunately most of these so-called remedies are ineffective, with the exception of a peroxide formula or other remedies that break down the odor’s main chemicals.

Keeping skunks as pets is legal only in certain states with the striped skunk (Mephitis mephitis), being the most social species and the one most commonly kept as a pet. When a skunk is kept as a pet, its scent gland can be surgically removed-good idea. As previously indicated the typical life spans for domesticated skunks are longer than for wild individuals.

Skunk Control. One of the first steps in preventing skunk problems around homes and other structures is eliminating situations that attract them, namely dog or cat food left outside for family pets. In addition many problems around homes and farms can be prevented by excluding skunks from spaces beneath buildings. Skunks can be prevented from living or entering under buildings and other structures by closing all spaces with wood or metal screen. These spaces should be tightly enclosed somewhat below ground level in order to inhibit or discourage digging. If skunks are already living under a building, they can be coerced to leave by the following steps: 1) Seal all openings except the main skunk entrance using sturdy wire mesh (1/4-inch hardware cloth or similar materials) to screen. If the entrance is not known tracking powder or a fine layer of sand, flour, or dust can be placed at suspected entrances. 2) After dark, when the skunk has left seeking food, it will leave tracks at the den entrance. Once a skunk has left the building, immediately seal the entrance with a hardware cloth "door." Do not permanently exclude skunks at this point as there may be more than one present. 

The temporarily one-way ½ inch hardware cloth door can be constructed by making it larger than the existing entrance and placing it outside the entrance. It should be hinged at the top and loose on the other three sides. Skunks will push it open to leave, but cannot re-enter. Once it has been determined that all skunks are out, the opening can be permanently sealed. Again, wire screens or other materials used to block the entrance should extend several inches below the ground to prevent the skunk from digging under it. Young skunks may remain in the den from April through August. Be sure all animals are out before sealing up the entrance. Moth balls or moth flakes (naphthalene or paradichlorobenzene) scattered or placed in porous cloth bags suspended in the den area, or liquid ammonia solution in a shallow pan, may discourage skunks from returning. Bright lights placed under buildings may serve a similar function.

The presence of skunks near farms or other structures can sometimes avoided by removing brush, wood piles and other sources of shelter. A 3 foot high, o1inch square mesh poultry netting fence can exclude these pests from gardens, schoolyards, landscaped areas, and similar locations. The bottom 12 inches of this structure should be below the surface of the ground and extend 6 inches down and then 6 inches outward thus forming the shape of an “L.” This will greatly discourage most of these pests from digging under it. Only rarely will skunks climb such a fence.

skunk trap
Live traps such as a Spray Proof Skunk Trap may be used to trap and remove skunks.

Trapping Skunks. There is obviously a special problem when trapping skunks. However, skunks don't typically spray if they can't see their target. It is best to wrap such traps with canvas or burlap before they are set. Traps should be baited with fish (canned or fresh), fish-flavored cat food, chicken parts, bacon, or peanut butter on bread. The trap should be set in the trail immediately in front of the burrow's main entrance. Logs, twigs, boards, or stones placed on either side of a path between the burrow opening and the trap will aid in funneling the animal toward the trap. All traps should be checked in the morning and early evening. Once captured, carefully pick up the covered trap and place it gently in the back of a pickup truck for transporting elsewhere. Avoid sudden, jarring movements or loud noises which may frighten the skunk. It is much more difficult to handle spotted skunks successfully in this manner, but striped skunks seldom release scent when these precautions are used. Trapped skunks can be transported 10 miles or more and released.

Certain states have laws that prohibit releasing trapped skunks thus requiring them to be killed. If permitted, in order to release a trapped skunk, it is good idea to stand more than 20 feet away and open the trap door using a string or fishing line. This is not generally recommended because of the potential for spreading rabies if by chance the captured animal is infected. Never release a skunk that shows signs of aggression, very nervous activity or salivation. It may be rabid and should be destroyed.

Shooting Skunks. It is not recommended to shoot skunks because it often results in release of their odor. Also, this is not recommended if the skunk needs to be captured for rabies testing.

Virginia Opossum (Didelphis virginiana)

The Virginia opossum, also known as the North American opossum, is the only marsupial known to occur in North America above of the Rio Grande. This is a solitary and nocturnal species that is about the same size of a domestic cat. It is quite common and very resourceful as a successful opportunist and occurs throughout Central and North America east of the Rockies ranging from Costa Rica northward to southern Ontario. It was introduced into California in 1910, and now is very commonly found in much of the Pacific Coast. Its ancestors originated in South America, but invaded North America via the Great American Interchange with the formation of the Isthmus of Panama about 3 million years ago. It is extremely common in towns and cities and can commonly be seen running along fences, feeding in garbage cans, or as road kill.

File:Opossum 2.jpg
Virginia Opossum. Image courtesy of Cody Pope.CC BY-SA 3.0

This species should not be confused with the possums of Australia, whose name is derived from a similarity to the Virginia Opossum, and are also marsupials, but of a totally different order. The Australian possum is one of the major mammalian pests of that country. This opossum is not only the largest of its genus but also the largest family and order. They are up to 20 inches in length and weigh up to 13 pounds. Their coats are a dull gray/brown with a distinctively white face. These pests have hairless, long prehensile tails which are capable of grabbing branches and carrying small objects. Opossums have opposable, clawless thumbs on their hind legs and up to 50 sharp teeth. 

Tracks of this species are typically indicated five finger-like toes in both the front and hind prints. The hind tracks are unusual and distinctive due to the opossum's opposable thumbs, which generally prints at an angle of 90 degrees or greater to the other fingers (sometimes near 180 degrees). Individual adult tracks generally measure 1⅞ inches long by 2 inches wide for the fore prints and 2½ inches long by 2¼ inches wide for the hind prints. Opossums have claws on all fingers fore and hind feet; these generally show in the tracks but may not. In a soft medium, such as the mud, the foot pads will be clearly visible.

The Virginia opossum is well known for feigning death when threatened, hence the term "playing possum." However, with this species, the behavior appears to be quite involuntary, and is apparently triggered by extreme fear. It is wise to not consider this as an indication of docility. Under serious threat, this marsupial will respond ferociously with screeching, hissing, and bearing its teeth. But with enough stress, the animal will enter a near coma which can last for a few hours. In this condition, the opossum lies on one side with its tongues hanging out, mouth and eyes open, emitting a green fluid from its anus and producing an odor that is seemingly disgusting to most predators. Besides discouraging large predators, playing possum also seems to convey to large animals that this animal is not a potential threat to their young.

Opossums are totally omnivorous and eat a wide range of plants and animals such as insects, fruits, eggs, dog food, and other small animals. Ripened persimmon fruit seems to be one of the opossum's favorite foods. In captivity, these pests are reportedly cannibalistic, though this is definitely uncommon in the wild.

The Virginia Opossum does not hibernate, although it may seek shelter during cold spells. Opossums, like most marsupials, typically have short lives for their size. The Virginia Opossum has a maximum life span in the wild of only about two years. In captivity, these pests live only about four years. One island population that was isolated for thousands of years in the absence of natural predators reportedly had up to 50% longer life spans than other opossum populations. .

Probably even more than raccoons, opossums are common in urban environments where they eat pet food, rotten fruit, and any of a number of types of human food including garbage. Some people consider opossums as rodents, but these marsupials are not closely related to rodents. They rarely, if ever, transmit diseases to humans and are seemingly resistant to rabies, mainly due to their low body temperatures compared to most mammals.

Control. There are a variety of repellent type chemicals that are commercially available that can be used to repel these critters from attics, and other locations. Although these have their place for the homeowner, most pest control applicators rely on trapping to totally eliminate long term problems.

If opossums are living in the near vicinity of a home, it is a good idea to trap them. Ultimately, they will reproduce and their offspring at one time or another will eventually move inside the home with the attic being the most likely location. One common mistake once they have established inside the attic is to try to seal them off. Sealing them in will often make the animal angry and aggressive, and they will do anything to escape, sometimes ending up inside the living quarters of the home. Animals sealed outside of the structure will just chew their way back in.

Unlike some vertebrates, opossums are relatively easy to trap. There are a number of commercial live traps that are available for this purpose. Trap placement doesn’t necessarily have to be in the established path of these animals. However, they should be placed in the vicinity of their activity. For example they could be placed in an attic, crawl space next to the foundation or even next to a tree that they climb to gain access to the attic. There are commercial baits that are available but fresh bait is also quite effective. If the animals have been eating fruits or vegetables, then it might be worthwhile to use similar items for bait. Raccoons are especially fond of eggs, meat, and fish.

True/False Questions 

20. Skunks are not true hibernators in the winter, but den up for extended periods of time. However, they remain generally inactive and feed rarely, going through a “dormant stage”.

21. Muscles located next to the scent glands allow skunks to spray with a “high degree” of accuracy, as far as 6.6 to 16 feet.

22. Skunks are reluctant to “use this weapon” (spray), as they carry just enough of the chemical for “5 or 6 uses”—about 15 cc—and require some 10 days to produce another supply.

23. Contrary to popular belief, raccoons eat active or large prey such as “birds and mammals” only occasionally, since they prefer prey which is easier to catch, specifically fish and amphibians. 

24. When trapping a skunk, the trap should be set in the “trail immediately” in front of the burrow's main entrance.

25. It is not recommended to shoot skunks because it often results in release of their odor. Also, this is not recommended if the skunk needs to be captured for rabies testing.

26. If permitted, in order to release a trapped skunk, it is good idea to stand more than 20 feet away and open the trap door using a string or fishing line. This is not generally recommended because of the potential for spreading rabies if by chance the captured animal is infected.

27, Never release a skunk that shows signs of aggression, very nervous activity or salivation. It may be rabid and should be destroyed.

28. 64. The Virginia opossum is noted for its “reaction to” threats, which is to feign death.

29. Unlike some other vertebrates, opossums are relatively easy to trap.

30. Opossums, like most marsupials, typically have short lives for their size. The Virginia Opossum has a maximum life span in the wild of only about 5 years.