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Rats and Mice

Roof Rat

Description

A blackish (or brownish), medium-sized, slender rat with long, naked, scaly tail; tail usually longer than head and body but not always so. External measurements average: total length, 14 inches; tail, 7.5 inches; hind foot, 1.4 inches. Weight, up to 3/4 lb.

Habits

Roof rats live in close association with man. They seldom become established as feral animals as do the Norway rats.

They inhabit grocery and drug stores, warehouses, feed stores, and poultry houses and are very common in cotton gins and associated grain warehouses. They may live near the ground, but usually they frequent the attics, rafters, and crossbeams of the buildings. They make typical runways along pipes, beams or wires, up and down the studding, or along the horizontal ceiling joists, often leaving a dark-colored layer of grease and dirt to mark their travel ways.

Like the Norway rat, the roof rat is largely nocturnal and only where populations are relatively high does one see them frequently in the daytime.

They feed on a wide variety of food items, including grains, meats, and almost any item that has nutritional value.

Roof rats breed throughout the year, with two peaks of production - in February and March and again in May and June. The period of least activity is in July and August. The gestation period is approximately 21 days, and the number of young per litter averages almost seven. They mature rather rapidly, are weaned when about 3 weeks old, and are able to reproduce when approximately 3 months old.

The roof rat is destructive to property and foodstuffs. Also, it plays an important part in the transmission of such human diseases as endemic typhus, rat bite fever, and bubonic plague.

Norway Rat

Description

Similar to the roof rat but larger and chunkier; tail shorter than length of head and body. External measurements average: total length, 18 inches; tail, 8 inches; hind foot, 2 inches. Weight, 14 - 18 oz.

Habits

The Norway, or Brown Rat lives both in close association with man and in the feral state, chiefly where vegetation is tall and rank and affords adequate protection. For example, the marshy lands on the coast of North Carolina offer ideal habitat for them.

As a commensal this rat lives principally in basements, on the ground floor, or in burrows under sidewalks or outbuildings.

Although more at home on the ground, these rats are adept at climbing and have been observed traveling along telephone wires from one building to another. In places they become exceedingly numerous and destructive.

They feed on a variety of items including both plant and animal materials. All sorts of garbage appear to be welcome, but their main stay is plant material. Grains of various sorts are highly prized. When established around poultry houses, they feed extensively on eggs and young chickens. They even have been known to kill lambs and young pigs!

House Mouse

Description

A small, scaly-tailed mouse with a distinct notch in the cutting surface of upper incisors (seen best in side view); hair short; ears moderately large and naked; upperparts ochraceous, suffused with black; belly buffy white, or buffy, usually without speckling and with slaty underfur; yellowish flank line usually present; tail brownish with black tip, not distinctly bicolor, but paler on underside; ears pale brown, feet drab or buffy, tips of toes white. Mammae in four or five pairs. External measurements average: total length, 6.5 inches; tail, 3.5 inches; hind foot, 3/4 inch. Weight of adults, 1/2 - 3/4 oz..

Habits

Although not native to North America the house mouse, since its early accidental introduction at most of our seaport towns, has become widespread throughout the United States and occurs either as a commensal or feral animal in practically all parts of the United States.

As commensal animals, house mice live in close association with man - in his houses, outbuildings, stores, and other structures. Where conditions permit, feral mice may be found in fields, along watercourses, and in other places where vegetation is dense enough to afford concealment. These feral animals make runways through the grass, or they may utilize runways made by rats and other meadow-inhabiting species. In the agricultural regions where irrigation is practiced house mice often are found in the vegetation along irrigation ditches, sometimes sharing common runways with native mice.

Although largely nocturnal, house mice are moderately active during the day, chiefly in their quest for food. In the wild they feed on a variety of plant material, including seeds, green stems, and leaves. Alfalfa hay, either in shocks or in stacks, affords an ideal source of food supply and, consequently, it is frequently infested with these mice.

House mice feed on practically any type of food suitable for the use of man or beast. They are particularly obnoxious around granaries, feed houses, and stores and may do considerable damage in destroying or contaminating food supplies intended for human consumption. In addition they will feed on such animal matter as insects and meat when available.

These mice are exceedingly prolific breeders. As many as 13 litters can be produced in one year. The number of young per litter averages about six. The gestation period is approximately 19 days, varying from 18 to 20. At birth the young mice are nearly naked with their eyes and ears closed. They develop rapidly; at the age of 3 weeks they are fully weaned and at the age of 4 weeks some of the young females are ready to assume family duties, although the average age of sexual maturity is about 35 days in females and 60 days in males. With commensals, breeding occurs throughout the year although it is somewhat curtailed in the colder months. In the wild state breeding appears to be restricted to the period from early June to late fall.

Although these mice are destructive when allowed to run free, they are widely used in laboratories as subjects for biological, genetic, and medical studies. When ranging free, however, they do a considerable amount of damage although they are not nearly so troublesome as the introduced rat.