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 ♦ Escambia, Santa Rosa and Baldwin Counties ♦

 

                    RODENTS

                             (MICE & RATS)

                                                        


MOUSE


Identification and Range: The house mouse (Mus musculus) is a small, slender rodent that has a slightly pointed nose; small, black, somewhat protruding eyes; large, scantily haired ears, and a nearly hairless tail with obvious scale rings. The adult mouse weighs about 2/5 to 4/5 ounces. They are generally grayish-brown with a gray or buff belly. Similar mice include the white-footed mice and jumping mice( which have a white belly), and harvest mice (which have grooved upper incisor teeth.)  Native to central Asia, this species arrived in North America along with settlers from Europe and other points of origin. A very adaptable species, the house mouse often lives in close association with humans and therefore is termed one of the "commensal" rodents along with Norway and roof rats. Following their arrival on colonists’ ships, house mice spread across North America and now are found in every state including coastal areas of Alaska, and in the southern parts of Canada.

Habitat: House mice live in and around homes, farms, commercial establishments, as well as in open fields and agricultural lands. The onset of cold weather each fall in temperate regions is said to cause mice to move into structures in search of shelter and food.

Food Habits: House mice eat many types of food but prefer seeds and grain. They are not hesitant to sample new foods and are considered "nibblers," sampling many kinds of items that may exist in their environment. Foods high in fat, protein, or sugar may be preferred even when grain and seed also are present. Such items include bacon, chocolate candies, butter and nutmeats. A single mouse eats only about 3 grams of food per day (8 pounds per year) but because of their habit of nibbling on many foods and discarding partially eaten items, mice destroy considerably more food than they consume. Unlike Norway and roof rats, they can get by with little or no free water, although they readily drink water when it is available. They obtain their water needs from the food they eat. An absence of liquid water or food of adequate moisture content in their environment may reduce their breeding potential.

General Biology, Reproduction, and Behavior: House mice are mainly nocturnal, although at some locations considerable daytime activity may be seen. Seeing mice during daylight hours does not necessarily mean there is a high population present, although this usually is true for rats Mice have poor eyesight, relying more on their hearing and their excellent senses of smell, taste and touch. They are considered essentially colorblind.

House mice can dig and may burrow into the ground in fields or around structures when other shelter is not readily available. Nesting may occur here or in any sheltered location. Nests are constructed of fibrous materials and generally have the appearance of a "ball" of material loosely woven together. These nests are usually 4 to 6 inches in diameter.  Litters of 5 or 6 young are born 19 to 21 days after mating, although females that conceive while still nursing may have a slightly longer gestation period. Newborn mice are naked and their eyes are closed. They grow rapidly and after 2 w3eeks they are covered with hair and their eyes and ears are open. They begin to make short excursions from the nest and eat solid food at 3 weeks. Weaning soon follows, and mice are sexually mature as early as 6 to 10 weeks old.

Mice may breed year-round and a female may have 5 to 10 litters per year. Mouse populations can therefore grow rapidly under good conditions, although breeding and survival of young slow markedly when population densities become high.

During its daily activities, a mouse normally travels an area averaging 10 to 30 feet in diameter, seldom traveling further than this to obtain food or water. Mice constantly explore and learn about their environment, memorizing the locations of pathways, obstacles, food and water, shelter and other elements in their domain. They quickly detect new objects in their environment, but they do not fear novel objects as do rats.  This behavior should be remembered if faced with a large population of mice in a residential, industrial or agricultural setting.  Proper placements of MOUSE BAIT is a must if you are to have a successful baiting program.


NORWAY RAT


Identification and Range


The Norway rat (Rattus norvegicus) is a stocky burrowing rodent, unintentionally introduced to North America by settlers who arrived on ships from Europe. First introduced into the United States about 1775, this rat has now spread throughout the contiguous 48 states. The Norway rat is found generally at lower elevations but may be found wherever humans live. Also called the brown rat, house rat, barn rat, sewer rat, gray rat, or wharf rat, it is a slightly larger animal than the roof rat. The nose is blunt, the ears are small, close set and do not reach the eyes when pulled down. The tail is scaly, semi-naked and shorter than the head and body combined. When distinguishing the Norway rat from the Roof rat, pull the tail back over the body. The tail of the Roof rat will reach the nose. The tail of the Norway rat will not reach beyond the ears. Adult Norway rats weigh an average of about 1 pound. Their fur is coarse and usually is brownish or reddish-gray above, and whitish-gray on the belly. Blackish individuals occur in some locations.

Habitat:

Food Habits:

General Biology, Reproduction and Behavior:

Rats have poor eyesight beyond three or four feet, relying more on their hearing and their excellent senses of smell, taste and touch. Norway rats are very sensitive to motion up to 30-50 feet away. They are considered essentially colorblind.

Rats use their keen sense of smell to locate food items and apparently to recognize other rats. Norway rats rely on their sense of smell to recognize the odors of pathways, members of the opposite sex who are ready to mate, differentiate between members of their own colonies and strangers, and to tell if a stranger is a strong or weak individual.

Norway rats use hearing to locate objects to within a few inches. This highly developed sense (combined with their touch sensitivity) can pinpoint someone rolling over in bed to a six inch area. The frequency range of their hearing (50 kilohertz or more) is much higher than that of humans (about 20 kilohertz.)

Norway rats have a highly developed sense of touch due to very sensitive body hairs and whiskers which they use to explore their environment. Much of a rodent’s movement in a familiar area relies heavily on the senses of touch and smell to direct it through time-tested movements learned by exploration and knowledge of its home range. Rodents prefer a stationary object on at least one side of them as they travel and thus commonly move along walls, a fact which is very useful when designing a control program.

Their sense of taste is excellent, and they can detect some contaminants in their food at levels as low as 0.5 parts per million. This highly developed taste sensitivity may lead to bait rejection if the rodent baits are contaminated with insecticide odors or other chemicals.

Norway rats usually construct nests in below-ground burrows or at ground level. Nests may be lined with shredded paper, cloth, or other fibrous material.

Litters of 6 to 12 young are born 21 to 23 days after conception. Newborn rats are naked and their eyes are closed, but they grow rapidly. They can eat solid food at 2 1/2 to 3 weeks. They become completely independent at about 3 to 4 weeks and reach reproductive maturity at 3 months of age, sometimes as early as 8 weeks.

Female Norway rats may come into heat every 4 or 5 days, and they may mate within a day after a litter is born. The average female rat has 4 to 6 litters per year and may successfully wean 20 or more offspring annually.


When eliminating Norway rats, remember that glue boards are not very effective on large rodents.  Snap traps and live traps will work.   The most effective control method for these rats is the use of weather proof bait blocks.  For more information on control of Norway rats:

Norway rats are primarily nocturnal. They usually become active about dusk, when they begin to seek food and water. Some individuals may be active during daylight hours when the rat population is high, when disturbed (weather change, construction, etc.) or when their food source is threatened. The territories of most rats are between 50 and 150 feet radius of the nest. In populations where there are many rats and abundant food and shelter, the territories will be towards the lower end of the range. If need be, however, rats will travel 300 feet or more daily to obtain their food and water. In urban areas most rats remain around the buildings and yards which provide their necessities, and unless they are disturbed, they do not move great distances.Norway rats will eat nearly any type of food. When given a choice, they select a nutritionally balanced diet, choosing fresh, wholesome items over stale or contaminated foods. They prefer cereal grains, meats and fish, nut, and some types of fruit. Rats require 1/2 to 1 ounce of water daily when feeding on dry foods but need less when moist foods are available. Food items in household garbage offer a fairly balanced diet and also satisfy their moisture needs.Norway rats live in close association with people. They burrow to make nests under buildings and other structures, beneath concrete slabs, along stream banks, around ponds, in garbage dumps, and at other locations where suitable food, water, and shelter are present. On farms they may inhabit barns, granaries, livestock buildings, silos, and kennels. In urban or suburban areas they live in and around residences, in cellars, warehouses, stores, slaughterhouses, docks, and in sewers. Although they can climb, Norway rats tend to inhabit the lower floors of multi-story buildings.


ROOF RAT


Identification:

The roof rat (Rattus Rattus) is one of two introduced rats found in the contiguous 48 states. The NORWAY RAT is the other species and is better known because of its widespread distribution. When distinguishing the Norway rat from the Roof rat, pull the tail back over the body. The tail of the Roof rat will reach the nose. The tail of the Norway rat will not reach beyond the ears.  A third rat species, the Polynesian rat, is present in the Hawaiian Islands but not on the mainland. Rattus Rattus is commonly known as the roof rat, black rat or ship rat. Roof rats were common on early sailing ships and apparently arrived in this country by that route. This rat has a long record as a carrier of plague.

Three subspecies have been named, generally identified by their fur color:

  1. The black rat, R. Rattus Rattus Linnaeus, is black with a gray belly.
  2. The Alexandrine rat, R. Rattus alexandrinus Geoffroy has an agouti (brownish streaked with gray) back and gray belly.
  3. The fruit rat, R. Rattus frugivorus Rafinesque, has an agouti back and white belly.

Crossbreeding between subspecies has often occurred, resulting in unreliability in identification by color. However, Roof rats do not cross with Norway rats.

Range:

Roof rats range along the lower half of the East Coast and throughout the Gulf States and upward into Arkansas. They also exist along the Pacific Coast and are found on the Hawaiian Islands. The roof rat is apparently not quite as adaptable as the Norway rat, which is one reason it has not spread throughout the country. Its geographic distribution suggests it is more suited to tropical and semi-tropical climates. Occasionally isolated populations are reported from areas not within their normal distribution range; however, these instances are rare. Most of the Great Plains states are free of roof rats but infestations can occur.

Habitat:

Roof rats are more aerial than Norway rats in their habitat selection and often will live in trees or on vine covered fences. Landscaped residential or industrial areas provide good habitat, as does vegetation of riverbanks and streams. They will often move into sugarcane and citrus groves. Roof rats are sometimes found living in or around poultry or other farm buildings as well as in industrial sites where food and shelter are available. Being agile climbers, Roof rats frequently enter buildings from the roof or accesses near utility lines which they use to travel from area to area. They have been found in sewer systems, but this is not very common.

Feeding Habits:

The food habits of roof rats resemble those of tree squirrels, since they both like a wide variety of fruit and nuts. They also feed on a variety of ornamental and native plant materials. Like the Norway rat, they are omnivorous and will feed on most anything if necessary. Roof rats usually require water daily, though their local diet may provide an adequate amount if high in water content.

Reproduction and Development:

Born in a nest about 21 to 23 days after conception, the young rats are naked and their eyes are closed. The 5 to 8 young in the litter develop rapidly, growing hair within a week. When they are 9 to 14 days old, 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 age of the rat. The young may continue to nurse until 4 or 5 weeks old. 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. In tropical or semitropical regions, the breeding season may be nearly year-round. Usually the peaks in breeding occur in the spring and fall.

Feeding Behavior:

Roof rats usually begin searching for food shortly after sunset. If the food is in an exposed area and too large to be eaten quickly, yet not too large to be moved, they will usually carry it to a hiding place before eating it. Many rats will cache or hoard considerable amounts of solid food, which they may or may not eat later. When necessary, roof rats will travel considerable distances for food. They can often be seen at night running along overhead utility lines. They may live in trees or attics and climb down to a food source. This is important from the standpoint of control, for traditional baiting or trapping on the ground or floor may intercept very few roof rats. Roof rats have a strong tendency to avoid new objects in their environment and this can influence control efforts. These rats may take several days before they will approach a bait station or trap.

Senses:

Rats see poorly, relying more on smell, taste, touch and hearing. They are considered to be colorblind, responding only to the degree of lightness and darkness of colors.  Roof rats also have an excellent sense of balance. They use their tails for balance while traveling along overhead utility lines and are very agile climbers.