Rats and Mice


4 Credits Category: 7A, 7D, 8

The roof rat, Norway rat and house mouse are frequently referred to as commensal rodents In the strictest sense of the term, this is somewhat of a misnomer. Commensal according to the dictionary refers to an organism (in this case the rodent) that lives in a symbiotic relationship where one species benefits (the rodents again) while other (humans) are not affected by their presence. Of course these rodents greatly benefit by the presence of humans but certainly their presence does adversely effects humans. Rats and mice have adapted to and benefit greatly by the presence of humans.  In doing so they have become one of the most successful groups of wild mammals, at least from the standpoint of survival.  This guide is not designed to recommend any pest control product.  Products mentioned are given as examples only.  Hopefully the guide will help the applicator to apply pest control techniques in a safe and effective manner.

Identification of Commensal Rodents. Identification of the pest is an integral part of any pest control scheme. The 3 principal species of domestic rodents in the United States are the roof rat (Ratus ratus), Norway rat (Ratus norvegicus) and the house mouse (Mus musculus).  These are fairly simple to distinguish from each other.  The following descriptions are based on adults. The Norway rat is the largest of the 3 species and is also commonly known as the brown, house, wharf and sewer rat.  Adult body length varies from 7 1/2 to 10 inches with a 6 to 8 ½ inch tail. The body fur is quite coarse and brown dorsally with black scattered hairs and a gray to white underside.  The snout or muzzle is relatively blunt with small closely set ears. They bear semi-naked bicolored tails (darker above and lighter below).




Differences in appearance of commensal rodents. Image Courtesy U.S. Department Health, Education and Welfare. Public Domain.

The roof rat is smaller than the Norway with a combined head and body length of 6 to 8 ½ inches and tail length of  6 to 8 ½.  Since there is an overlap in total head and body length between the 2 species, a more reliable identifying characteristic is the ratio of head + body length to tail length.  The tail of the roof rat is longer than its combine head-body length, while that of the Norway rat is shorter.  In addition the snout of the roof rat is pointed.  Finally the roof rat’s ears are comparatively larger than those of the Norway.

Of course the house mouse is much smaller than adult rats with a head-body length ranging from 2 ½ to 3 ½ inches and tail length from 3 to 4 inches.  The house mouse can be confused with young rats as both are similar in appearance.  Mice eyes and feet are relatively smaller than those of young rats of approximately the same size.

Roof ratNorway RatHouse mouse

Roof Rat (left), Norway rat (middle) and house mouse (right). Images courtesy of CDC.

Scats or Fecal Pellets. Since these critters are nocturnal and quite secretive, the operator may need to determine the presence of rodents by means other than their physical presence. As these rodents move through a structure, they indiscriminately drop fecal pellets or scats and readily urinate. One rat is capable dropping over 25,000 fecal pellets in a 1-year period . Adult Norway and roof rat scats are the shape of and about twice the size of a grain of rice; however, Norway rat droppings have smooth round ends while roof rat dropping have pointed ends.  As might be expected, the overall size of scats vary with the size and age of the rat but in any infestation there will likely be some adults present.  Mice droppings are small, black, oval-shaped and about the size of a grain of rice.  Large roach droppings look the same as mice droppings, so be careful not to confuse the two. If in doubt a hand lens examination will reveal hair in mice scats while those of large cockroach exhibit longitudinal grooves and certainly do not bear hairs..


Attic Full of Roof Rat Scats.

Smudges. Once established rats develop favored runway as they travel throughout a structure.  They rarely deviate from the runways.  In addition these runways are typically located next to walls or other vertical surfaces. The body hairs of rats are fairly oily in nature; consequently, as a rat moves through a structure, some of this oil rubs off onto the walls and other nearby objects.  Over time this oil will appear as smudge marks or dark streaks.


 Smudge (oil) Marks on Pipe and an Attic Full of Rat Urine.

Urine. Under ultraviolet light, urine and to a lesser extent rat hairs glow.  Fresh urine appears as bluish-white while older urine glows yellow.  These marks may be spotty or in some cases appear as  “squiggly line”, since rats urinate while moving. There are several hand-held ultraviolet light devices available. There are other materials that also produce fluoresce under UV light.  These include bleached fabrics, bleaches and ever tar products to name a few.  However, if an infestation is substantial, there is no mistaking rat urine as it will be very prominent-to say the least.

Blacklight, Portable blacklight

Hand-help Ultraviolet Light.

Gnawing. One sure sign of a rodent infestation is significant gnawing on any of a number of hard objects or items. One characteristic of rodents in general is their extraordinary hard incisor teeth, 2 uppers and 2 lowers that butt against each other.  These teeth grow continuously and must wear down.  As a result rat and mice continually gnaws to gain access into walls, doors, packages, water pipes and outdoor irrigation systems.  They also use this gnawing to collect nesting materials.


Roof Rat Gnawing of PVC Pipe.

The nature of damage to outdoor vegetation can often provide clues as to whether it is caused by the roof or Norway rat. Other rat signs may also assist, but be aware that both species may be present. Setting a trap to collect a few specimens may be the only sure way to identify the rat or rats involved. Out-of-doors, roof rats may be present in low to moderate numbers with little sign in the way of tracks droppings, runs and burrows.

There is less of a tendency to see droppings, urine, or tracks on the floor in buildings because rats may live overhead between floors, above false ceilings, or in utility spaces, and venture down to feed or obtain food. In food-storage facilities, the most prominent signof an infestation may be smudge marks, the result of oil and dirt rubbing off of their fur as they travel along their aerial routes.

The adequate inspection of a large facility for the presence and location of roof rats often requires a nighttime search when the facility is normally shut down. Use a powerful flashlight to spot rats and to determine travel routes for the best locations to set baits and traps. Sounds in the attic are often the first indication of the presence of roof rats in a residence. When everyone is asleep and the house is quiet, the rats can be heard scurrying about.

Behaviors Important to Control.  As the term implies, neophobic mean the fear of new things.  While roof rats and Norway rats are definitely neophobic, the house mouse exhibits almost the opposite behavior. While the house mouse is likely to poke around a newly placed bait station or trap, a rat is more likely to be very suspicious and avoid them when possible.  When rats enter a new environment for nesting or feeding, they become very familiar with all objects and soon can move around by what is termed kinesthesis or muscular memory.  Once establish, they can quickly move through a structure with an automatic memory of what is in their path.

The inquisitive nature of the house mouse makes them easier to trap or bait than rats.  A new trap in a mouse’s environment is readily inspected as are bait stations.  On the other hand, when a trap, glue board or bait station is first placed in the path of a rat, it is normally avoided for the first few days.  As the rat becomes more accustomed to its presence, it will eventually be accepted.  Of course this makes these rodents more difficult to control.  One common trick that applicators frequently use when confronted with this behavior is to place a trap in the rat’s environment, but not set it until the rat becomes accustomed to its presence.  Of course the same thing can be accomplished by not uncovering a glue board for the first few days.

Rats usually begin searching for food shortly after sunset. If the food is in an exposed area and too large to be eaten quickly, but not too large to be moved, they will usually carry it to a hiding place before eating it. Many rats may cache or hoard considerable amounts of solid food, which they eat later. Such caches may be found in a dismantled wood pile, attic, or behind boxes in a garage.

When necessary, roof rats will travel considerable distances (100 to 300 feet) for food. They may live in the landscaping of one residence and feed at another. They can often be seen at night running along overhead utility lines or fences. They may live in trees, such as palm, or in attics, and climb down to a food source. Traditional baiting or trapping on the ground or floor may intercept very few roof rats unless bait and/or traps are placed at the very points that rats traverse from above to a food resource.

This reminds me of a story that was told to me by my friend Bert Lopez of Univar Corporation.  He was called into a situation at one of the more popular restaurants in Southern California.  Apparently there was a single dominant male rat in the restaurant that was raising total havoc.  Several operators were called in but nobody could eliminate the rat.  It was totally neophobic and had a total run of the restaurant knowing everything in the place very well.  After much thought, Bert found out that the main diet of the rat was pecan pies which were kept on a rack in the back of the restaurant.  So Bert simply had the pastry chef bake a rat trap in a pecan pie.  The pie was placed on the same location where the rat fed every night. He got him the first night.

Habitat. Roof rats are more aerial than Norway rats in their habitat selection,- and often live in trees or on vine-covered fences. Landscaped residential or industrial areas provide good habitat, as doe’s riparian vegetation of riverbanks and streams. Parks with natural and artificial ponds, or reservoirs may also be infested. Roof rats will often move into sugarcane and citrus groves. They are sometimes found living in rice fields or around poultry or other farm buildings as well as in industrial sites where food and shelter are available.

Roof rats frequently enter buildings from the roof or from accesses near overhead utility lines, which they use to travel from area to area. They are often found living on the second floor of a warehouse in which Norway rats occupy the first or basement floor. Once established, they readily breed and thrive within buildings, just as Norway rats do. They have also been found living in sewer systems, but this is not common.

Reproduction. The young are born in a nest about 21 to 23 days after conception. At birth they are hairless, and their eyes are closed. The 5 to 8 young in the litter develop rapidly, and  grow hair within a week. Between 9 and 14 days, their eyes open and they begin to explore for food and move about near their nest. In the third week, they begin to take solid food. The number of litters depends on the area and varies with nearness to the limit of their climatic range, availability of nutritious food, density of the local rat population, and the age of the young rats. Typically, 3 or more litters are produced annually. The young may continue to nurse until 4 or 5 weeks old. By this time they have learned what is good to eat by experimenting with potential food items and by imitating their mother.

Young rats generally cannot be trapped until about 1 month old. At about 3 months of age, they are completely independent of the mother and are reproductively mature. Breeding seasons vary in different areas. In tropical or semitropical regions, the season may be nearly year-round. Usually the peaks in breeding occur in the spring and fall. Roof rats prefer to nest in locations off of the ground and rarely dig burrows for living quarters, if off-the-ground sites exist.

Sense of Sight and Touch.  Rats have poor eyesight and rely on the sense of touch to a great degree when moving around. The main senses they rely on for navigation is the previously mentioned sense of kinesthesis and the sense of touch.  Rats have large oral vibrissae (whiskers) and many rather long stiff guard hairs that are mixed in with their fur.  They rely on both of these types of hair to sense or feel their environment.  Of course this is the reason why rats moving around a structure stick closely to vertical surfaces (walls, foundations of the house, cupboard, boxes, etc.) when establishing their runways.  They feel the structure next to them and avoid, if possible, moving away from their established path.

This is of the reason why when a trap, glue board or bait station is used for control, it is essential to place them in the rats already established path. Of course when the rat first encounters these new objects, it is very wary.  But on the other hand, it is very reluctant to move around the object thus leaving it established path. As a result it tests the new object to determine if it is safe to go over or through. It may nibble on it, feel it with its whiskers or sense it in some other way.  Depending on the age and experience of the rat, it will eventually become accustomed to this presence.  Older more experience rats tend to be more wary than younger ones.

Population Dynamics. Rat densities (numbers of rats in a given area) are determined primarily by the suitability of the habitat—the amount of available nutritional and palatable food and nearby protective cover (shelter or harborage). The great adaptability of rats to human-created environments and the high fertility rate of rats make for quick recuperation of their populations. A control operation, therefore, must reduce numbers to a very low level; otherwise, rats will not only reproduce rapidly, but often quickly exceed their former density for a short period of time. Unless the suitability of the rat’s habitat is destroyed by modifying the landscaping, improving sanitation, and rat-proofing, control methods must be unrelenting if they are to be effective.

Social Behavior. The social behavior of free-living roof rats is very difficult to study and, as a result, has received less attention than that of Norway rats. Most information on this subject comes from populations confined in cages or outdoor pens. Rats tend to segregate themselves socially in both space and time. The more dominant individuals occupy the better habitats and feed whenever they like, whereas the less fortunate individuals may have to occupy marginal habitats and feed when the more dominant rats are not present. Knowledge is limited on interspecific competition between the different genera and species of rats. At least in some parts of the United States and elsewhere in the world, the methods used to control rats have reduced Norway rat populations but have permitted roof rats to become more prominent, apparently because they are more difficult to control. Elsewhere, reports indicate that roof rats are slowly disappearing from localized areas for no apparent reason. It has often been said that Norway rats will displace roof rats whenever they come together, but the evidence is not altogether convincing.

Damage. In food-processing and food-storage facilities, roof rats do about the same type of damage as Norway rats, and damage is visually hard to differentiate. In residences where rats may be living in the attic and feeding outdoors, the damage may be restricted to tearing up insulation for nesting or gnawing electrical wiring. Sometimes rats get into the kitchen area and feed on stored foods. If living under a refrigerator or freezer, they may disable the unit by gnawing the electrical wires. In landscaped yards they often live in overgrown shrubbery or vines, feeding on ornamentals, vegetables, fruits, and nuts. Snails are a favorite food, but don’t expect roof rats to eliminate a garden snail problem. In some situations, pet food and poorly managed garbage may represent a major food resource.

In some agricultural areas, roof rats cause significant losses of tree crops such as citrus and avocados and, to a lesser extent walnuts, almonds, and other nuts. They often eat all the pulp from oranges while the fruit is still hanging on the tree, leaving only the empty rind. With lemons they may eat only the rind and leave the hanging fruit intact. They may eat the bark of smaller citrus branches and girdle them. In sugarcane, they move into the field as the cane matures and feed on the cane stalks. While they may not kill the stalk outright, secondary organisms generally invade and reduce the sugar quality. Norway rats are a common mammalian pest of rice, but sometimes roof rats also feed on newly planted seed or the seedling as it emerges. Other vegetable, melon, berry, and fruit crops occasionally suffer relatively minor damage when adjacent to infested habitat such as riparian vegetation.

Like the Norway rat, the roof rat is implicated in the transmission of a number of human diseases including murine typhus, leptospirosis, salmonellosis (food poisoning), rat-bite fever, and plague. It is also capable of transmitting a number of domestic animal diseases and is suspected in the transference of ectoparasites from one place to another.

Baits and Bait Stations. There are dozens of rat and mouse bait brands available on the market.  The toxicants in these baits fall into 2 broad categories, namely anticoagulants and non-anticoagulants.  Anticoagulants kill by rupturing capillaries and preventing blood from clotting.  As a result the effected rodents internally bleed to death.  This type of death although sounding quite gruesome actually is quite painless.  The anticoagulants fall into 2 categories also, namely first and second generation.  The first generation anticoagulants, as their name implies, are the older of the 2 groups.  These are sometimes also referred to as multiple feeding anticoagulants.  This simply means that the concentration of the toxicant in the baits is low enough that the animal must feed on them on several consecutive days to result in death.  These include Warfarin-the oldest, Diphacinone and Chlorophacinone. The second generation anticoagulants include Brodifacoum, Bromadiolone and Difethialone. These are referred to as the single feeding anticoagulants. This means that the toxicants in baits are high enough that a single feed will typically result in death.  Both types are somewhat slow acting requiring 3 to 10 days for death once a lethal dose is acquired.

There are 3 different toxicants used in rat and mouse baits that are non-anticoagulant in mode of action: however, the most common types used for control of these rodents are the anticoagulants.  Some of the non-anticoagulant types are restricted to outdoor agricultural rodent control.  These are zinc phosphid (discussed with gophers), cholecalciferol and bromethalin.  As far as which toxicant is most effective, this is a matter of opinion and the choice of which to use is up to the individual pest control company and beyond the scope of this article.  In all cases, if rodent baits are used the operator must read the label carefully.  The pesticide label is backed by years and research as to how to use these chemical in a safe and effective manner.  It cannot be emphasized enough-read the label carefully!

The use of poisons for control of rat in urban situations although effective does have some drawbacks.  These are all also toxic to nontarget mammals.  Dogs are readily attracted to many types of bait and can die from consumption of these materials-although much more would be required to cause death to these larger animals, as opposed to these rodents.  Also other mammals such as raccoons and opossums will also readily consume many rat baits.  As a result tamper resistant bait stations are now required for the use of rat bait in an outdoor situation.  Although non-tamper resistant baits stations can still be legally used indoors with rat baits, it is advisable to use tamper resistant types of sturdy bait stations indoors to prevent nontarget animals from accessing baits.

The EPA has come out with somewhat rough guidelines as to what criteria must be met to make a tamper resistant bait station.  They must be made of sturdy material that is not easily broken and fitted with internal devices (e.g. baffles) that keep the bait inside.  In addition they must have a lid that cannot be easily removed and should be able be secured to the surface on which they sit.  There are many types and sizes available.  Non-tamper resistant bait stations, if used indoors, are normally required to be placed in inaccessible locations to prevent bait access to pets and children.

Rat tamper proof bait stations

One of Many Types of Tamper Resistant Bait Stations.

A second problem exists with the use of rat baits especially in an indoor situation.  Although not as much of a problem with mice, one or more dead rat can cause a considerable odor problem.  This can occur in a wall void or any of a number of hard to reach areas in the home.  Of course homeowners are not happy when this occurs. One false belief that has circulated around the industry is that rodents poisoned with anticoagulant baits actively search for water and therefore most often die outdoors. This of course has no validity.  Another fallacy is that rats that are killed with anticoagulants tend to dehydrate or dry up and therefore do not produce an odor.

If odor problems do develop within a structure, there are deodorized products that are fairly effective in removing them. Some of these are enzyme based compounds that work 2 ways. Initially they "eats" the odor molecule which is a gaseous by-product emitted by the decaying rodent. Secondly they attach to and increase the density of the odor causing molecules. As a result the heavier molecules simply drop from the air.  Best results occur when these products are sprayed directly on the area where the animal died. If not these products can be sprayed into crawl spaces, attics and wall voids where you think the animal died.


One of several brands of odor killers.

Solid rodent baits come in 2 forms. One form is basically pellets or grains that are impregnated with the toxicant that come in a variety of flavors. The choice of flavor depends partially on which commensal rodent is targeted.  Norway rats reportedly prefer meat as they commonly eat large cockroaches, greases and other foods thrown away in dumpsters.  While roof rats commonly feed on fruits and nuts, they also readily accept insects, snails and grain.  Mice are grain feeders.  Needless to say all 3 species are quite omnivorous.  Choices as to which bait flavor to use may also depend on what the rodents are feeding upon at the initiation of the job.

The second formulation of rodent baits is produced by embedding the baits in paraffin block. These blocks are not only attractive to the rodents from feeding aspects, but are also attractive due to their gnawing habits.  These blocks have one advantage over the pelleted forms of bait.  Commensal rodents, especially Norway rats instinctively prefer to take their food to familiar and secure locations.  In addition they frequently hoard or store food in these locations.  This behavior presents a potential problem to the applicator/operator. That is toxic baits are now removed from the bait stations and now is found in some unprotected location in the structure.  Of course the paraffin blocks are more difficult to move to some other location and some baits station provided internal means of securing the blocks.

Another bait formulation that can be used for rodent control is liquid baits. Though not too effective for mice (since they are able to derive their water requirements from the food they eat), liquid bait works well for rats which are a problem in dry areas. Common areas where these might work well would be feed stores and pet shops. Like other poisons, placements must be away from children and pets. As with other types of baits there are tamper proof bait stations available for liquid baits. These stations should be placed up high, behind appliances, in cupboards, in attics or crawl spaces or generally out of the way where only rodents are likely to find them. This will help minimize accidental consumption by non-target animals.

Live Traps, Snap Traps and Glue Boards.  Live traps are more commonly and effectively used for mice than rats.  Because these devices do not kill or harm the rodent, they will not become afraid of it. Live trapping mice is easy, inexpensive and without risk or danger to non-target animals.  The latest design of traps will last a long time, catch many rodents and be effective on even the most experienced and wary rodent.  The Tin Cat and Mouse Master offer multiple catch capability for mice.  The author has used both Tin Cat and Mouse Monster and several times caught over 20 with a single setting. Mice of course are very curious and will readily be drawn to these traps.


Tin Cat.

The great thing about these traps is that they don't kill the animals so others do not become wary or afraid.  Reportedly a trap with several mice in it seemingly lure new ones.  The untrapped mice would come and circle the holding area seemingly interested with the activity going on inside.  The smell of food is so powerful that even after being trapped, the mice do not become upset or frightened. However, if they are left for any length of time and the food supply runs out, they will become frantic and distressed. It is important to place plenty of bait inside to insure the mice will remain quiet once trapped. If animals are left to die, they will certainly smell and decay resulting tap avoidance by other mice. An important factor to remember when trapping mice is that they do not range far from their nest or center of activity.  As a consequence, it is important to place these traps in close vicinity where mouse activity has been observed..

Glue boards or sticky traps add more tools to the applicator’s arsenal of control techniques. These traps vary in size and are placed alongside walls, around cabinets, under furniture and refrigerators. With rats they should be placed in their establish runways.  When the animal steps onto the glue, they get stuck and cannot pull free.  They usually will not quit and many times will pull a leg, tail or section of their body apart in an effort to escape.  This can cause a mess and  the applicators should take care in using these devices where young children are not likely to stumble upon such a mess. The author has encountered several mice and rats caught on these traps which were screaming! It was a loud, almost humanlike.  Generally speaking glue board and sticky trap will only work for a short time with significant rat populations.  Normally the applicator might catch a few rats the first day or two but the remaining population will quickly adjust their behavior to avoid the traps.  These are very smart animals.


One of Many types of Glue Boards.

This brings up the problem of animal rights individuals or just the homeowner who loves animals and has had a white pet rat that can be purchased in any pet store.  These domesticated rats do make nice pets, as they are very intelligent, readily recognize their owners and are quite friendly. Actually they are the same species as wild Norway rats but certainly not the same animal.   The wild Norway or roof rat is wary, readily bites and can vector several diseases to humans.  However, some customers do not recognize the difference between the two.  The point is that the white rat is a domesticated species and the other is wild.  A similar correlation could be made between our regular honeybee (which has also been domesticated by humans) and the killer or Africanized bee.  Almost everyone appreciate regular bees and the good they do but I doubt if anyone would want killer bees in their house.  The point is that the applicator has to know their customer and situation and use those control techniques that best fit the situation.  For example, you probably wouldn’t want to use glue traps in an office full of individuals all with different feelings about rodents.  It probably wouldn’t be good form for a rat or mouse lover or animal right activist to run across a glue trap full of screaming mice.  In that case, live trapping might be more acceptable.  You can drown the critters once you take them out of the office!

There are a variety of snap traps that are available for rat and mouse control.  All have basically the same design with a spring loaded lever that is pulled back and held in place with a trigger.  With the original design, the metal trigger was quite small.   Newer more effective designs have an expanded trigger. Both mice and rats will easily clean the bait off the old metal trigger traps, while this is more difficult with the new design. Another advantage is that these traps do not need bait.  Just place them alongside the wall or other vertical surfaces where rats have established their runways.  Be sure to locate the trigger closest to the wall. Such traps will catch 1 or 2 rodents (especially with rats) for initial cleanouts and preventive maintenance programs, but don't rely on them if you suspect more than a few animals. It is important to secure these traps.  If a rat or mouse is caught but not killed, it can pull the trap off to some undisclosed location.  Then once it dies, there is a potential odor problem.  Common locations for setting these traps for roof rats indoors include darkened corners of attics, suspended ceilings and other aerial locations where they feel safe. The use of baits with these traps will likely increase their catch ratio.  Common baits for roof rat are fruits and nuts while nuts, bacon or other meats work well for Norway rats.  Peanut butter is a favorite of all 3 species of commensal rodents. Some of the tamper-resistant bait stations are equipped with a compartment for snap traps.  This is an added bonus when dealing with dicey situations where dogs or children have the potential of getting some part of their body trapped.


A Snap Trap with Expanded Trigger.

Frightening Devices. Rats have acute hearing and can readily detect noises. They may be frightened by sound-producing devices for a while but they become accustomed to constant and frequently repeated sounds quickly. High-frequency sound-producing devices are advertised for frightening rats, but almost no independent research exists on their effects specifically on roof rats or Norway rats, as far as that is concerned. These devices must be viewed with considerable skepticism, because research has not proven them effective.  Lights (flashing or continuously on) may repel rats at first, but rats will quickly acclimate to them.

Fumigation.  Norway rats are basically burrowing rodents and live in tunnels or dens in the ground. Under certain situations, fumigation with aluminum phosphide (Fumitoxin, Phostoxin, Gastoxin) can be an effective control technique.  This is a Category 1 material and is a permit material in California.  It should be remembered that this material cannot be used any closer than 100 feet from an occupied structure.

Exclusion and Sanitation.   Part of a successful rat or mouse control program should be multifold.  With rats especially, a thorough examination of the property is advisable.  This examination not only serves to help delineate where ongoing control efforts should be applied, but may also be important from the standpoint of producing an infestation.  Certain conditions are conducive to the attraction of new rat problems once an existing infestation is eliminatedThese areas may include dumpsters, standing water, creeks, streams, neighboring businesses, fruit trees, heavy vegetation and drainage systems to name a few.  The most common attractants around the average home include either pet food or bird seed. The smells from these items are so strong, they will attract several types of animals to your yard, including rats. Once they get a taste of these nutritious foods, they will try to feed on them daily. In homes that have pets, there is a much more likelihood that rodent infestations will occur than in homes without. Pet food is packed with more nutrition now than ever as is bird seed and rodents are able to detect these food supplies.

If removal of some of these attractive food sources is going to be part of a rat pest management program, it is important not to do this prior to elimination of the existing population. If done prior to controling the rats,  these vermin will likely seek a new food source and of course the most desirable would likely be found inside the home.

Exclusion is undoubtedly one of the most important elements in a successful rodent control program. If in a populated area and there is a significant rodent problem(especially rats) problem, you cannot expect to eradicate them all.  Even if total control can be obtained in a structure, an infestation is likely to occur unless some type of exclusion programs is used.  Such a program has to be very well designed, as these rodents can enter a structure through the smallest openings.  Adult rats can squeeze through a crack 1/2 inch wide and an adult house mouse can fit through a hole the diameter of a pencil.  On part of exclusion techniques is to plug all gaps in the structure that exceed 1/2 inch and any hole larger than a quarter.

Exclusion techniques are aimed at preventing rats reaching the roof of structures (especially roof rats).  This can be especially difficult since roof rats can jump straight up 2 feet and horizontally 5 feet.  They are good swimmers and can climb most walls, telephone and electrical wires, trees and almost any other object in contact with the structure.  Gaps can be filled with steel wool, but this quickly rusts unless covered with cement, stuccos or similar materials.  Copper wool or a copper based material called Stuffit’s can be stuffed in holes or stretched across a wide gap.  There are foam based gap fillers but these may be susceptible to rat gnawing.

Besides filling holes exclusion techniques can and should possibly include any for the following:


Metal Barrier When Wires (Electrical, Telephone) Run Close to Structure.


Hardware Cloth Curtain Wall on a Storage Building. Top Edge Covered with Strip of Sheet Metal.


Blocking End Spaces of Wall Voids Using Sheet Metal, Brick or Cement Blocks


Rodent Proofing Openings around Pipes with Sheet Metal (left) and Concrete (right).


Rodent Proofing\Drains with Hardware Cloth


Rodent Proofing a Door, Placing Sheet Metal Channel at Bottom and Cuffs at Sides, Over Channel.


Rodent Proofing Vent with 1/4th Inch Hardware Cloth


Rodent Proofing Utility Wires to Limit Access to Buildings Using Rolling Plastic Tubes Made from Rectangular Sheets of Plastic.
The Tube Rolls When the Rodent Tries to Walk Over It.


Rodent Proofing Air Vents and Chimneys Using 1/4" Hardware Cloth.

It also important to advise customers on landscape design that should be changed, if possible.  Large trees and shrubs immediately adjacent to a structure are an easy access to the roof. Ivy is a preferred habitat of rats and large areas should be cut back and possibly removed, especially if it grows touching the home.  Any debris and piles of firewood stacked against the structure should be removed.

Cotton Rat. A cotton rat is any member of the genus Simoom. They are called cotton rats because they build their nests out of cotton and can damage cotton crops. Cotton rats have small ears dark coats and are found in North and South America. They are primarily herbivores. The molars of cotton rats are S-shaped when viewed from above. The genus name literally means S-tooth.  

File:Sigmodon hispidus1.jpg

Cotton Rat.  Image Courtesy CDC.

In California, known damage is limited to sugarbeets and citrus. Elsewhere their feeding has been reported on on cotton, grasses, alfalfa, grains, vegetables, fruit crops, squash, sugar cane, corn, sweet potatoes and melons. Cotton rat burrowing may cause leakage or breaks in canal banks. They readiyconsume  quail eggs and those of other ground nesting birds and compete with these birds for food.

These rats range from Mexico and Southern United States; in California the cotton rat is established in irrigated portions of the Imperial Valley and along the Colorado River.

They are dependent upon a dense stand of vegetation for both food and protection. Cotton rats occupy grassy fields and meadows, marshy areas, cactus patches, wastelands, and weedy roadsides and ditch banks. Salt marshes and mixed forests are also reported habitats in southeastern states.

Cotton rates may be detected by their well-defined runways and connecting burrows. Runways are about 3 inches across and burro openings are somewhat larger. Runways in active areas have small piles of freshly clipped vegetation and scattered or small piles of ½ inch long droppings. Their nests are built in shallow burrows or under rocks or logs or occasionally in abandoned  skunk and ground squirrel dens. Nest material includes dry grass, fibers stripped from stems of larger plants or other suitable material.

They can swim and do so with little hesitation. Their home range vatioes from ¼ and ¾ acres for females and 1 to 1 ¼ acres for males. Cotton rats are very excitable and pugnacious. Cotton rats are active year-round and do not store food for the winter. Although primarily nocturnal, they are often active in the day. Cotton rats are primarily vegetarians feeding on stems, leaves, roots, and seeds, but insects, carion and animal flesh are also readily eaten.

The reproductive capacity of cotton rats is exceedingly high; they are usually the most abundant mammal wherever they occur. Unmated females come into heat every 7 to 9 days and may mate within a few hours after giving birth. The gestation period is 27 days and several litters are produced annually (2 to 10, average 5.6). One to 12 young per litter have been recorded but 6 is average. The young are weaned at 10 to 15 days but they have been known to survive without their mother after 5 days of age. Most young breed for the first time at 2 to 3 months of age; some breed at 40 days. Several generations may be living in the same nest at one time. The average life span of a cotton rat is 6 months and they are considered full grown at the age of 5 months. Cotton rats are common prey of coyotes, foxed, weasels, skunks, hawks and owls.

Cotton rats are classified as nongame mammals by the California Fish and Game Code. Nongame mammals which are found to be injuring growing crops or other property may be taken at any time or in any manner by the owner or tenant of the premises. However, if leg-hold steel-jawed traps are used they shall not have saw-toothed or spiked jaws or have a spread of 5 ½ inches or larger without offset jaws. They may also be taken by officers or employees of the Department of Food and Agriculture or by federal or county officers or employees when acting in their official capacities pursuant to the provisions of the Food and Agricultural Code pertaining to pests.

Control Materials:

Baits: Crimped oat grouts are the most effecect bait, although crimped whole oats are at times accepted by cotton rats.

Toxicants: Zinc phosphide Spot Baiting – 1.00% Broadcast baiting – 2.00%. Lightly scatter teaspoon quantities of bait (about 80 baits per pound) in runways near active burrows.

Broadcast Baiting: Spread bait evenly by hand or mechanical spreader through the infested area at the rate of 5 to 10 pounds per acre, depending on the density of the infestation. Broadcast bait will fall through most vegetation to the ground surface. Do not apply bait where trees or grass are wet, or when rain is likely to occur within 24 hours.

Voles or Meadow Mice

Identification. Vole are small rodent resembling house mice but with stouter bodies, shorter hairy tail, slightly rounder heads and smaller ears and eyes.  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 Microbus californium and Microbus montana are economically important in the west.  M. californium 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

Voles are commonly mistaken for other small animals. Moles, gophers, mice, rats and even shrews have similar characteristics and behavioral tendencies.  Voles can create and will often times utilize old abandoned mole tunnels, thus confusing the applicator into thinking that moles are active. Voles to a high degree are nerbavors. Like shrews they will eat dead animals and like mice or rats, they can live on most any nut or fruit. Voles will readily "girdle" or eat the bark of small trees and ground cover much like a porcupine. This girdling can easily kill young plants and can be injurious to larger trees or other shrubs. Voles readily consume succulent root systems and will burrow under plants or ground cover to feed. Bulbs are another favorite target for voles. Voles eat a wide variety of plants, most frequently grasses and forbs. In late summer and fall, they store seeds, tubers, bulbs, and rhizomes.  They can become  pests of a variety of crops, especially when their populations are high. Occasional food items include snails, insects, and animal remains.

General Biology, Reproduction, and Behavior. Voles are active day and night, year-round. They do not hibernate. Home range is usually 1/4 acres  or less, but varies with season, population density, habitat, food supply, and other factors. Voles construct many tunnels and surface runways with numerous burrow entrances. A 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 reported population, there was 88% mortality during the first month of life.

Cyclic population dessities are characteristic of voles. Population levels generally peak every 2 to 5 years; however, these cycles are not predictable. Occasionally during population irruptions, extremely high densities are reached. Dispersal, food quality, climate, predation, physiological stress, and genetics have been reported to influence population levels. Other factors probably also play a part.  Very high densities may be reached during population irruptions. In Klamath Basin, Oregon, the montage vole densities ranged from 200 to 500 per acre and may have reached 4,000 per acre in some instances during a 1957 to 1958 irruption. Voles are prey for many predators (for example, coyotes, snakes, hawks, owls, and weasels); however, predators do not normally control vole populations.

With high population, these normally outdoor species can enter homes in fairly large numbers.  The author has experience this in his previous vertebrate control business.  On more than one situation, very large populations develop in O’Conner’s legume planted slopes. Estimated populations in these cases were several hundred per acre. Unfortunately rather expensive homes were located below and above these slopes.  It was quite common for random voles to accidentally enter these homes. Although voles rarely invade houses, in the event that they do, they can be controlled by setting snap traps or live traps (Sherman or box-type) as done for house mice.

Damage and Damage Identification. Voles may cause extensive damage to orchards, ornamentals, and tree plantings due to their girdling of seedlings and mature trees. Girdling damage usually occurs in fall and winter. Field crops (for example, alfalfa, clover, grain, potatoes, and sugar beets) may be damaged or completely destroyed by voles. Voles eat crops and also cause damage when they build extensive runway and tunnel systems. These systems interfer with crop irrigation by displacing water and causing levees and checks to wash out. Voles also can ruin lawns, golf courses, and ground covers with thier runways.

Girdling and gnaw marks alone are not necessarily indicative of the presence of voles, since other animals, such as rabbits, may cause similar damage. Vole girdling can be differentiated from girdling by other animals by the non-uniform gnaw marks. They occur at various angles and in irregular patches. Marks are about 1/8 inch wide, 3/8 inch long, and 1/16 inch or more deep. Rabbit gnaw marks are larger and not distinct. Rabbits neatly clip branches with oblique clean cuts. Examination of  girdling damage and accompanying signs such as feces, tracks, and burrow systems may be needed to identify the animal causing the damage.

The most easily identifiable sign of voles are extensive surface shallow runways with numerous burrow opening. The 1-to-2 inch wide surface runways through grass and other low growing vegetation indicates the presence of these mice. In an active infestation, these trails are littered with feces, pieces of stems, leaves and other leftovers. The runways lead to underground burrows that consist of short branching tunnels, food storage areas and nests.


Voles pose no major public health hazard because of their infrequent contact with humans; however, they are capable of carrying disease organisms, such as plague (Yesinia pestis) and tularemia (Francisilla tularensis). Be careful and use protective clothing when handling voles.

ControlHardware cloth cylinders exclude voles from seedlings and young trees. The mesh should be 1/4 inch or less in size. Bury the wire 6 inches to keep voles from burrowing under the cylinder. Large scale fencing of areas is probably not cost-effective. Drift fences with pit traps may be used to monitor populations and can indicate when voles are immigrating to crops, orchards, or other cultivated areas.

Cultural and habitat modification practices can reduce the likelihood and severity of vole damage. Eliminate weeds, ground cover, and litter in and around crops, lawns, and cultivated areas to reduce the capacity of these areas to support these pests. Lawn and turf should be mowed regularly. Mulch should be cleared 3 feet or more from the base of trees. Voles can live in dense populations in ditch banks, rights-of-way, and water ways that are unmanaged. Adjacent crop can be cost-effectively protected by controlling vegetation through mowing, spraying, or grazing. Soil tillage is effective in reducing vole damage as it removes cover, destroys existing runway-burrow systems and kills some voles outright. Because of tillage, annual crops tend to have lower vole population levels than perennial crops. Voles are nevertheless capable of invading and damaging annual crops, especially those that provide them with cover for extended periods of time.

Zinc phosphide is the most commonly used toxicant for vole control. It is a single-dose toxicant available in pelleted and grain bait formulations and as a concentrate. Zinc phosphide baits generally are broadcast at rates of 6 to 10 pounds per acre or are placed by hand in runways and burrow openings. Although prebaiting (application of similar non-treated bait prior to applying toxic bait) is not usually needed to obtain good control, it may be required in some situations, such as when a population has been baited several times and bait shyness has developed. Zinc phosphide baits are potentially hazardous to ground-feeding birds, especially waterfowl. Placing bait into burrow openings may reduce this hazard.

Anticoagulant baits are also effective in controlling voles. Anticoagulants are slow-acting toxicants requiring from 5 to 15 days to take effect. Multiple feedings are needed for most anticoagulants to be effective. In many states, one or more anticoagulant baits are registered for controlling voles.

In addition to broadcast and hand placement, anticoagulant baits also can be placed in various types of bait containers. Water repellent paper tubes with an anticoagulant bait glued to the inside surface make effective, disposable bait containers. Tube size is about 5 inches (12 cm) long by 1 1/2 inches (4 cm) in diameter. Bait containers protect bait from moisture and reduce the likelihood of non-target animals and small children consuming bait.

Fumigants usually are not effective because the complexity and shallowness of vole burrow systems allow the fumigant to escape. They may work in new, small burrow systems with only one or two entrances.

Trapping is not effective in controlling large vole populations because time and labor costs are prohibitive. Mouse snap traps can be used to control a small population by placing the trap perpendicular to the runway with the trigger end in the runway. A peanut butter-oatmeal mixture or apple slices make good baits. Fall and late winter are periods when many vole species are easiest to trap.

A wide variety of predators feed on voles. Voles are relatively easy for most predators to catch and are active, and therefore available, day and night year-round. Despite their vulnerability and availability, voles are not usually “controlled” by predators. This is because voles have a high reproductive potential. Postpartum breeding is common and females may breed as early as 2 weeks of age. Synchronous breeding also occurs. These factors enable voles to increase at a faster rate than predators (Pearson 1985).

Deer Mice. Peromyscus maniculatus and Peromyscus leucopu

The scientific name for a deer mouse and its 66 subspecies is Peromyscus maniculatus.  They are all 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 leucopuse.  Because the 2 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 very often used for laboratory experimentation due to their self-cleanliness and easy care.  Deer mouse came to the attention of the public when it was discovered to be the primary reservoir species for Hantavirus.  These mice also serve as important reservoirs of bubonic plague and Lyme’s disease.

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

Identification.  The deer mouse is one of the most familiar rodents found in North America. Deer mice are named for their coats, which resemble the coat of the white-tailed deer. They have white bellies and dark gray or brown backs and heads.  Characteristically they are darker at their back and gradually lighten in color at the underside and legs. These mice measure approximately 6 inches from nose to tail. The tail and body are approximately the same length. Their tails are brown at the tip and white near the base. The deer mouse's ears are large, round and almost hairless. Their eyes are also comparatively large giving them a good sense of sioght.  They weigh between 15 and 32 grams. Many people refer to deer mice as "field mice".

Biology and Distribution.   Deer mice can be found in most parts of the United States except the southeastern states. They are common in rural and semi-rural areas with weeds, tall grass and plentiful vegetation. Their burrows and tunnel systems are much simpler than those created by other species. They use dry grass, weed stems, fur and feathers to construct their nests. Deer mice are blind, pink and hairless at birth. They weigh between 1 and 3 grams and begin to change color within 24 hours. On the third day after birth, the ears unfold. Eyes open within 2 weeks and young are weaned at 4 weeks. New fur exhibits faintly blue coloration, which fades as they age and disappears completely when deer mice are sexually mature. 

Deer mice are primarily herbivorous, but will also consume caterpillars, spiders and grasshoppers on occasion. They readly and consume grains, seeds, nuts and berries. As such, deer mice are formidable pests on farms and in the crop-yielding countryside.  In winter, these mice enter homes in search of food and warmth. Although they become sluggish during cold months, they do not hibernate. Deer mice hoard food supplies and actively forage clsoe to their nesting sites. 

Damage. Hantavirus.  Because they are known reservoirs of Hantavirus, these mice are potentially extremely dangerous. The Hantavirus Pulmonary Syndrome (HPS) is spread when mouse droppings, urine, or carcasses are disturbed. The HPS becomes airborne and is inhaled by people in the area. Deer mouse droppings are primarily seen in mouse runways: near cupboards, drawers and other food storage areas. They are smooth with pointed ends and measure between 1/8 and 1/4-inch in length. In the span of 6 months, a pair of mice is capable of consuming 4 pounds of food and producing 18,000 fecal pellets. The removal of these droppings can prevent the spread of mouse-borne diseases. Utmost care must be taken when handling mouse droppings. The use of facemasks and gloves are highly advisable. It is recommended that the droppings, carcass, and the adjacent are be sprayed with disinfectant before sweeping. It is best not to vacuum the droppings because this may increase the release of Hantavirus into the air.

Hantavirus has probably caused people to get sick for years in the United States, but it was not recognized until recently. In 1993 there was an outbreak of fatal respiratory illness on an Indian reservation at the border of Utah, Colorado, New Mexico, and Arizona. Researchers discovered that Hantavirus caused the epidemic. Since that discovery, Hantavirus disease has been reported in every western state, and in many eastern states. As previously indicated, it is carried by rodents, especially deer mice. The virus is in their urine and feces, but it does not make the carrier animal sick. Humans are thought to become infected when they are exposed to contaminated dust from mice nests or droppings. The disease is not passed between humans. People may encounter contaminated dust when cleaning long-empty homes, sheds, or other enclosed areas.

The U.S. Centers for Disease Control and Prevention (CDC) reported that rodents carrying Hantavirus have been found in at least 20 national parks. The CDC says it is possible that the virus is in all of the parks. The CDC suspects that campers and hikers may be more likely to catch the disease than most people. This is because they pitch tents on the forest floor and lay their sleeping bags down in musty cabins. So far, however, only a couple of cases have been directly linked to camping or hiking. Most people who are exposed to the virus have come in contact with rodent droppings in their own homes.

The early symptoms of Hantavirus disease are flu-like (fever, chills, muscle aches). For a very short period of time, the infected person starts to feel better. Then, within 1 - 2 days, the person may develop shortness of breath. The disease gets worse quickly and leads to respiratory failure.

Other symptoms may include: Dry cough; General ill feeling (malaise); Headache; Nausea and vomiting; Rapid shallow breathing.

A doctor may notice signs of: Acute respiratory distress syndrome (ARDS); Decreased blood pressure (hypotension; Decreased levels of oxygen in the blood (hypoxia), causing the skin to have a bluish color (cyanosis); Kidney failure

An effective treatment for Hantavirus infection involving the lungs is not yet available. Hantavirus hemorrhagic fever that involves the kidneys (with renal syndrome) does respond to treatment with ribavirin given through a vein (intravenously). This medication shortens the illness and reduces the risk of death. Treatment must be given in the hospital. Often patients are admitted to an intensive care unit. Oxygen therapy is used. Blood gases are closely monitored. Severe cases will need respiratory support with a breathing tube (endotracheal tube) and ventilator. Hantavirus is a serious infection. Even with aggressive treatment, more than half of the cases are fatal.

Lyme Disease. This is a bacterial illness caused by a bacterium called a "spirochete." In the United States, the actual name of the bacterium is Borrelia burgdorferi. In Europe, another bacterium, Borrelia afzelii, also causes Lyme disease. Certain ticks found on deer harbor the bacterium in their stomachs. Lyme disease is spread by these ticks when they bite the skin, which permits the bacterium to infect the body. Lyme disease is not contagious from an affected person to someone else. Lyme disease can cause abnormalities in the skin, joints, heart, and nervous system.

Lyme disease only became apparent in 1975 when mothers of a group of children who lived near each other in Lyme, Connecticut, made researchers aware that their children had all been diagnosed with rheumatoid arthritis. This unusual grouping of illness that appeared "rheumatoid" eventually led researchers to the identification of the bacterial cause of the children's condition, what was then called "Lyme disease"in1982. It has now been found in the 48 continental United States and is the most prominent tick borne disease.  It has been likened to syphilis because of its lengthy developmental cycle.  The disease is not sexually transmitted but can be passed from mother to fetus.  It has been found in 51 of the 58 counties of California and is most known north of San Francisco.  The Eastern states with the highest outbreaks are New York, New Jersey, and Maine.  At the time of this writing Lyme disease has been found in an isolated location of Southern California.

This disease affects different areas of the body in varying degrees as it progresses. The site where the tick bites the body is where the bacteria enter through the skin. As the bacteria spread in the skin away from the initial tick bite, the infection causes an expanding reddish rash that is often associated with "flu-like" symptoms. Later, it can produce abnormalities in the joints, heart, and nervous system. It is medically described in three phases as: (1) early localized disease with skin inflammation; early disseminated disease with heart and nervous system involvement, including palsies and meningitis; and (3) late disease featuring motor and sensory nerve damage and brain inflammation as well as arthritis.

In the early phase of the illness, within days to weeks of the tick bite, the skin around the bite develops an expanding ring of upraised redness. There may be an outer ring of brighter redness and a central area of clearing, leading to a "bull's-eye" appearance. This classic initial rash is called "erythema migrans" (formerly called erythema chronicum migrans). Patients often can't recall the tick bite (the ticks can be as small as the periods in this paragraph). Also, they may not have the identifying rash to signal the doctor. More than one in four patients never gets a rash. The redness of the skin is often accompanied by generalized fatigue, muscle and joint stiffness, swollen lymph nodes ("swollen glands"), and headache resembling symptoms of a virus infection.

The redness resolves, without treatment, in about a month. Weeks to months after the initial redness of the skin, the bacteria and their effects spread throughout the body. Subsequently, disease in the joints, heart, and nervous system can occur. In early Lyme disease, doctors can sometimes make a diagnosis simply by finding the classic red rash (described above), particularly in people who have recently been in regions in which Lyme disease is common. The doctor might review the patient's history and examine the patient in order to exclude diseases with similar findings in the joints, heart, and nervous system. Blood testing for antibodies to Lyme bacteria is generally not necessary or helpful in early stage disease, but it can help in diagnosis in later stages. (Antibodies are produced by the body to attack the bacteria and can be evidence of exposure to the bacteria. Antibodies, however, can be false indicators of disease, since they can remain for years after the disease is cured. Moreover, false-positive tests in patients with nonspecific findings (those that are not specifically suggestive of Lyme disease) can lead to confusion. Currently, the confirmatory test that is most reliable is the Western Blot assay antibody test. More accurate tests are being developed. Generally, Lyme blood testing is helpful in a patient who has symptoms compatible with Lyme disease, who has a history of a tick bite at least a month prior, or who has unexplained disorders of the heart, joints, or nervous system that are characteristic of Lyme disease.

Because Lyme disease is transmitted by ticks attaching to the body, it is important to use tick-bite avoidance techniques when visiting known tick areas. Spraying insect repellant containing DEET onto exposed skin can help. Wearing long pants tucked into boots and long sleeves can protect the skin. Clothing, children, and pets should be examined for ticks. Ticks can be removed gently with tweezers and saved in a jar for later identification. Bathing the skin and scalp and washing clothing upon returning home might prevent the bite and transmission of the disease.

There are various mammalian reservoirs of the disease that include rodents, deer and humans.  Unfortunately, only about 1/4 of the cases are reported and there are false-positive laboratory results.  There is no lasting immunity to the disease and antibiotics only work in the first stage of the disease.  Under laboratory conditions mosquitoes and biting flies have vectored this disease.

Most cases of Lyme disease are curable with antibiotics. This is so true that some authors of Lyme disease research have stated that the most common cause of lack of response of Lyme disease to antibiotics is a lack of Lyme disease to begin with! The type of antibiotic depends on the stage of the disease (early or late) and what areas of the body are affected. Early illness is usually treated with medicines taken by mouth, for example, doxycycline (Vibramycin), amoxicillin, or cefuroxime axetil. Therefore, if a person finds a typical bull's-eye skin rash (described above) developing in an area of a tick bite, they should seek medical attention as soon as possible. Generally, antibiotic treatment resolves the rash within one or two weeks with no long-term consequences. Later illness such as nervous-system disease might require intravenous drugs; examples are ceftriaxone (Rocephin) and penicillin G.

For the relief of symptoms, pain-relieving medicines might be added. Swollen joints can be reduced by the doctor removing fluid from them. An arthrocentesis is a procedure whereby fluid is removed from a joint using a needle and syringe under sterile conditions. It is usually performed in a doctor's office. Rarely, even with appropriate antibiotics, the arthritis continues. It has been suggested by researchers that sometimes joint inflammation can persist even after eradication of the Lyme bacteria. This has been explained as an ongoing autoimmune response causing inflammation of the joint that was initially stimulated by the original bacterial infection. The doctor also can use oral medications such as ibuprofen (Motrin, Nuprin) to reduce inflammation and improve function.

The later phases of Lyme disease can affect the heart, causing inflammation of the heart muscle. This can result in abnormal heart rhythms and heart failure. The nervous system can develop facial muscle paralysis (Bell's palsy), abnormal sensation due to disease of peripheral nerves (peripheral neuropathy), meningitis, and confusion. Arthritis, or inflammation in the joints, begins with swelling, stiffness, and pain. Usually, only one or a few joints become affected, most commonly the knees. The arthritis of Lyme disease can look like many other types of inflammatory arthritis and can become chronic. Researchers have also found that anxiety and depression occur with an increased rate in people with Lyme disease. This is another important aspect of the evaluation.


Early Symptoms of Lyme Disease, a Rash Called Erythematic Migrans.  Image Courtesy CDC Photo Library.

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. Neptpma 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.

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 stealing 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.

File:Neotoma fuscipes - Pacific Grove Museum of Natural History - DSC06663.JPG

Left. A Wood or Pack Rat. Image Courtesy Daderot CCO-Public Domain..  Right Pack Rat Nest. Image Courtesy Toiyabe at the English language Wikipedia CC BY-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.

On occasion humans are bitten by assassin bug bites.  A professor friend of mine caught me in the hall and asked if I had any ideas as what bit him last night.  I had an idea but first asked him what he did last weekend. He lives in the foot hills.  He indicated that he had wood rats on his property and got tired of them stealing coins, jewelry and other shiny items.  He decided to destroy their nests on his property to get them to leave.  Well that worked OK and the wood rat left but the assassin bugs that also lived in the nest of the pack rats no longer had an immediate source of food (pat rat blood).  As a result, some invaded his house and had a feast of human blood.  As illustrated in the following image, assassin bug bites typically result in large red blotch with a puncture wound (due to insertions of their relatively large Piercing sucking mouthparts) in the middle.  They frequently are linear with a few in a row.

Biology. These critters are strictly nocturnal and feed on a variety of plant materials, including seeds, nuts, acorns, green vegetation, fruit, fungi or whatever else is available.  Their nests are built in brush, trees, around tree stumps, in cliffs or in rock crevices.  The nest typically has several entrances and multiple chambers, including a potty hole (okay, YOU come up with a better word. I guess bathroom wold be OK but a little anthropomorphic).  Some pack rats build auxiliary nests in a tree adjacent to the ground habitat. The home range of pack rats is relatively small and rarely exceeds 250 feet.

Breeding season varies depending on species, area and season, but a single brood a year of 2 to 5 young is typically produced in the spring.  The young stay with the mother until almost fully grown. Then they move on to a new location, build a new one or the mother leaves to construct a new nest.  Rarely do pack rat populations exceed 20 to an acre.

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

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.

Version 1. C E U Credit Test.

1.  The 3 principal species of domestic rodents in the United States are the roof rat (Rattus rattus), Norway rat (Rattus norvegicus) and the house mouse (Mus musculus).

2.  The Norway rat's snout or muzzle is relatively blunt. It also has small, closely set ears and a semi-naked bicolored tail (darker above and lighter below). The Norway rat is considerably stockier than the roof rat weighing nearly twice as much. 

3. The tail of the roof rat is longer than its combine head-body length while that of the Norway rat is shorter.

4. The house mouse can be confused with young rats as both are similar in appearance.  Mice eyes and feet are relatively smaller than those of young rats of approximately the same size.

5. Adult Norway and roof rat scats are the shape of and about twice the size of a grain of rice,  Norway rat droppings have smooth pointed ends while the roof scats have round ends.

6. The body hairs of rats are fairly oily in nature; consequently, as a rat moves through a structure, some of this oil rubs off onto the walls.  Over time this oil will appear as smudge marks or dark streaks.

7. Under ultraviolet light rat urine and to a lesser extent rat hairs will glow.  Fresh urine appears as bluish-white while older urine glows as yellow.

8. Rat teeth grow continuously and must wear down.  As a result, rats and mice continually gnaw to gain access into walls, doors, packages, water and outdoor irrigation systems.

9. Rat densities (numbers of rats in a given area) are determined primarily by the suitability of the habitat including the amount of available nutritional and palatable food and nearby protective cover (shelter or harborage)

10. In some agricultural areas, roof rats cause significant losses of tree crops such as citrus and avocados and, to a lesser extent, walnuts, almonds, and other nuts.

11. While the house mouse pokes around a newly placed bait station or trap, a rat is more likely to be very suspicious of new objects in its path and avoid them when possible.

12. Rats have poor eyesight and don’t rely on the sense of touch to a great degree when moving around.

13. On common trick that applicators frequently use when confronted with neophobic behavior of rats is to place a trap in the rat’s environment but not set it until the rat becomes accustomed to its presence.

14.  Rats have large oral vibrissae (whiskers) and many rather long stiff guard hairs that are mixed in with their fur.  They rely on both of the types of hair to sense or feel their environment.

15. Rats have acute hearing and can readily detect noises. They may be frightened by sound-producing devices for a while but they become accustomed to constant and frequently repeated sounds quickly. Regardless these types of devices are quite effective for rat control.

16. The concentration of the toxicant in first generation anticoagulants baits is low enough that the animal must feed on them on several consecutive days to result in death.  These include Warfarin-the oldest, Diphacinone, Zinc Phosphide and Chlorophacinone.

17. Though not too effective for mice (since they are able to derive their water requirements from the food they eat), liquid bait works well for rats which are a problem in dry areas.

18. Live traps are more commonly and effectively used for rats than mice.

19. Adult rats can squeeze through a crack 1/2 inch wide and an adult house mouse can fit through a hole the diameter of a pencil.  On part of exclusion techniques includes plugging  all gaps in the structure that exceed 1/2 in and any hole larger than a quarter.

20. Rats can jump straight up 2 feet and horizontally 5 feet.  They are good swimmers and can climb most walls, telephone and electrical wires, trees and almost any other object in contact with the structure. 

21. Voles close the openings of their tunnels with earthen plugs.

22. The main means of controlling large populations of voles is broadcasting zinc phosphide baits at 5 to 10 pound per acre or spot treatment with zinc phosphide or anticoagulant baits (the later may not be time efficient).

23. A symptom of the presence of voles is shallow runways in grass and other vegetation.

24. The later phases of Lyme disease can affect the heart, causing inflammation of the heart muscle. This can result in abnormal heart rhythms and heart failure.  

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

26.  Meadow mice are nocturnal and typically have 1 or 2 generations per year and will readily "girdle" or eat the bark of small trees and ground cover much like a porcupine. This girdling can easily kill young plants and is not healthy for trees or other shrubs.

27.  Girdling and gnaw marks alone are not necessarily indicative of the presence of voles, since other animals, such as rabbits, may cause similar damage.

28.  Vole girdling can be differentiated from girdling by other animals by the non-uniform gnaw marks. They occur at various angles and in irregular patches. Marks are about 1/8 inch wide, 3/8 inch long, and 1/16 inch or more deep.

29. In winter, deer mice enter homes in search of foodand water.

30. Because deer mice are known reservoirs of Hantavirus, they are potentially extremely dangerous. The Hantavirus Pulmonary Syndrome (HPS) is spread when mouse droppings, urine, or carcasses are disturbed. This virus has not been fouind in California.

31. Deer mice feces are smooth with pointed ends and measure between 1/8 and 1/4-inch in length. In the span of 6 months, one pair of mice is capable of consuming 4 pounds of food and producing 18,000 fecal pellets

32. Deer mice hoard food supplies and actively forage for food near their nesting sites. 

33. Besides girdling certain types of shrubs, voles under certain conditions enter homes.

34. Wood rat populations number are typically quite low and as a result their feeding activity is not a proble to agriculture of landscaping.

35. 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.

36. Pack rats get their name from the fact that they will enter homes and steal shiny objects such as coins and jewelry.

37. Wood rats typically produce as many 20 offspring per year as do voles.

38. Compared to many rat species, wood rats are easily trapped.  This can be accomplished by placing a standard wood based rat trap baited with a prune,nutmeats or raisins near the nest or runways.

39.The home range of pack rats is relatively small and rarely exceeds 250 feet.

40. Broadcasting anticoagulant baits such as chlorophacinone or diaphacinine are effective against wood rats.