Commensal Rodents

Norway rat, Rattus norvegicus

The three species of commensal rodents (those that live primarily around human habitation) are Norway rats, roof (black) rats, and house mice. These omnivorous rodents consume millions of bushels of grain each year in the field, on the farm, in the elevator, mill, store, and home, and in transit. They also waste many more millions of bushels by contamination. These rodents typically drop 25 to 150 pellets and void 1/3 to 2/3 ounce (10 to 20 ml) of urine every 24 hours and constantly shed fine hairs.

Rats cause extensive damage to sugar-cane in Hawaii and Florida, and roof rats are serious pests in Hawaiian macadamia nut plantations. These rodents will feed on poultry chicks and occasionally even attack adult poultry, wild birds, newborn pigs, lambs, and calves. Health departments annually report hundreds of human babies bitten by rats. Many viral and bacterial diseases are transmitted to humans by rodent feces and urine that contaminate food and water (Weber 1982).

Gnawing by rodents causes considerable property damage. Fires are some-times started when rats and mice gnaw the insulation of electric wiring. They will also use materials such as oily rags and matches for building nests, which can result in fires by spontaneous combustion. Extensive damage to foundations and concrete slabs is sometimes done when Norway rats burrow under buildings. Burrows into dikes and outdoor embankments cause erosion.

Signs of commensal rodents are gnawing, droppings, tracks, burrows, and darkened or smeared areas along walls where they travel. Reviews of problems caused by these species and methods of control are provided by Meehan (1984), Jackson (1987), Baker et al. (1993), Marsh (1994), and Timm (1994).

Summary of Damage Prevention and Control Methods

Exclusion

Seal all openings larger than 1/2 inch (1.3 cm) wide.

Habitat Modification

Good sanitation practices reduce sources of food, water, and shelter. Store foodstuffs in rodent-proof structures or containers.

Store and dispose of refuse and garbage properly.

Control weeds and remove debris from around structures.

Frightening

Ultrasonic devices have not been proven to control rats.

Repellents

Ropel^®.

Toxicants

Anticoagulant rodenticides (slow-acting chronic-type toxicants) Brodifacoum (Talon^®). Bromadiolone (Maki^®, Contrac^®). Chlorophacinone (RoZol^®). Diphacinone (Ramik^®, Ditrac^®). Pindone (Pival^®, Pivalyn^®) Warfarin (Final^® and others).

Toxicants other than anticoagulants (may be acute or chronic toxicants) Bromethalin (Assault^®, Vengeance^®). Cholecalciferol (Quintox^®). Red Squill. Zinc phosphide (Ridall Zinc^®, ZP^® rodent bait).

Fumigants

In some situations, outdoor burrow fumigation may be effective. Aluminum phosphide (Phostoxin^® and others). Chloropicrin. Gas cartridges. Methyl bromide.

Trapping

Snap traps. Live traps. Glue boards.