Damage and Damage Identification

Muskrat, Ondatra zibethicus

Muskrats most often cause problems where people have created or manipulated wetlands or where wetlands border agricultural crops. The most serious damage results from burrows in pond dams, levees, and irrigation canals. The burrow entrance is below water level and penetrates the embankment at an upward angle to allow for a room above the water level. Damage is increased when the water level rises and the burrow is extended higher to provide a dry chamber, thereby increasing chances of wash-outs and cave-ins. At times, muskrats cause severe damage to grain, such as rice, and to garden crops growing near water. Muskrats are primarily vegetarians, but they will feed on aquatic animals where vegetation is limited (Miller 1994).

Muskrats commonly construct cone-shaped houses projecting 6 inches to 3 feet (15 to 90 cm) above the water surface. Muskrat presence is indicated by houses and burrow entrances. Under-water runs can be observed when the water is clear or after a winter draw down of ponds or reservoirs (Miller 1994).

Summary of Damage Prevention and Control Methods

Exclusion

Riprap the inside of a pond dam face with rock, or slightly overbuild the dam to certain specifications.

Cultural Methods and Habitat Modification

Eliminate aquatic vegetation as a food source.

Draw down farm ponds during the winter months.

Frightening

Seldom effective in controlling serious damage problems.

Repellents

None are registered.

Toxicants

Zinc phosphide. Anticoagulants (state registrations only).

Trapping

Body-gripping traps (Conibear® No. 110 and others).

Leghold traps, No. 1, 1 1/2, or 2.

Where legal, homemade “stove pipe” traps also are effective when properly used.

Shooting

Effective in eliminating some individuals.

Other Methods

Integrated pest management.