The Norway rat (left) has a blunt snout and small ears, while the roof rat (right) has a pointed snout and large ears.



Under the right conditions, a house mouse (below) can live for two years or more.



Order: Rodentia
Family: Muridae

Commensal Rodents

Rats and mice have lived with humans since prehistoric times because we provide the basic necessities for them (shelter, food and nesting materials). They are among the most significant pests to humans, destroying billions of dollars' worth of food annually. It has been estimated that between one-fifth to one-third of the world's food supply never reaches the table due to losses from rodents. They also contaminate foods with their droppings and are a major concern to food and health professionals.

Rats and mice have also been known to bite humans in heavily infested areas. They can incur serious damage to structures, equipment, furniture, utilities and transportation vehicles through their insistent gnawing. They can chew through water pipes, and can cause major power outages and fires.

Rats and mice are important as vehicles for harboring and rapidly transporting diseases. In the past century, more than 10 million people have died from rodent-borne diseases. Some of the major diseases they have been associated with include plague, rickettsial diseases, leptospirosis, rat bite fever, trichinosis, hantavirus, rabies and bacterial food poisoning.

Despite their health threat to and hatred by many people, rats and mice are very beneficial as research animals and are an important food source for both animals and some groups of people.

Description

In the United States, the three most important species are the Norway rat (Rattus norvegicus), the black or roof rat (Rattus rattus) and the house mouse (Mus musculus, also referred to as Mus domesticus).

The Norway rat is large and robust, weighing in at about seven to 18 ounces. It has a blunt snout, small ears covered with short hairs, brown shaggy fur and a belly that is gray to yellowish white in color. It is found throughout the U.S.

The roof rat is sleek and graceful, and weighs about five to nine ounces. It has a pointed snout, large hairless ears, and its fur is smooth and brownish-gray to black. Its belly can be white, gray or black. This species is found in the South Central and Eastern states, and along the entire West Coast.

The house mouse is small, slender and weighs only about 0.4 to one ounce. It has a pointed snout, large ears with hair, and its fur is light brown to light gray and smooth. It can be found throughout the U.S.

Biology

Norway and black rats have litter sizes of six to 12 young, but up to 22 pups have been recorded. The gestation period ranges from 21 to 25 days, with a female typically producing three to six litters in her lifetime. Under ideal conditions, females may give birth every 24 to 28 days. Young rats become sexually mature at about three months, with most living six months to a year.

Under optimum conditions, a house mouse may live two years or more, and can breed throughout the year. A female has a gestation period of 18 to 21 days, and produces a litter ranging from two to 13 mice. A long-lived female may produce six to 10 litters.

Control

Several methods should be used to achieve control of rats and mice. Sanitation and mechanical alteration is the first step. Eliminate food, water and harborage areas. Keep trash and debris in tightly closed containers, and possible nesting materials out of reach. Sometimes, pruning trees and shrubs close to the structure may be necessary. Keep rats and mice out by rodent-proofing the structure by eliminating and sealing off all dead spaces, cracks, crevices and other openings. Fill void areas with concrete, or stuff with steel wool. Cover openings with sheet metal.

Traps and baits can be used, but will only offer temporary control if the previous steps are not taken. There are many types of traps available, including snap traps, sticky traps and live traps. These should be placed in areas likely to be visited by rodents. Because some of these are baited with food as an attractant, they should not be left out for long periods of time.

Anticoagulants are usually used in baits, which cause the rodent to bleed to death internally once it is consumed. Because these products can affect humans in the same way, never place them in areas where children and pets can contact them. Rodent poisons should not be left out for long periods of time, and dead rodent carcasses should be removed immediately.

 Last updated on   02/17/08 11:33:55 AM