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Controlling rats and mice presents challenge for many farms and ranches

by Wyoming Livestock Roundup

Rats and mice can raise havoc with buildings and their contents. 

Robert M. Timm, Ph.D and Extension Wildlife Specialist emeritus at the University of California Hopland Research and Extension Center, says rat and mouse problems are mostly associated with barns and other structures, feed bunks or feed storage areas. 

“In insulated buildings, a lot of damage from mice may go unnoticed until they have destroyed insulation in the walls or ceiling. Rats or mice may gnaw insulation off wires, causing electrical problems or fires. They may also damage chewable parts in tractors and other equipment,” he says.

Vehicles and equipment

Mice and rats may damage wiring in vehicles and farm equipment. 

  “They may disable machinery by chewing wires and creating shorts or gnawing off drive belts, cooling system hoses, etc. Rodents cause a diverse number of problems, and often by the time we notice a problem, there has already been a lot of damage done,” Timm says.

He continues, “We may see a few rats or mice but don’t do anything about it until it becomes a major problem. In those cases, we often spend more time and money repairing things and trying to control a large population than if we’d paid more attention earlier, when there were fewer rodents.”


Since they like to live in barns, feedlots, grain storage facilities, etc., there is food readily available for them most of the year, making it difficult to attract them to poison baits. 

“With pets or livestock present, it’s difficult to find appropriate places to locate bait stations or traps. Therefore, one of the keys to control rats and mice is to try to keep structures tight enough that it’s hard for them to get in,” Timm comments.

Ranchers don’t want mice and rats in the walls or attics where they are not easily seen but create a lot of damage. 

“It may be almost impossible to eliminate food sources, so another tactic is to eliminate shelter for these rodents – any place that they might nest, hide from predators, or remain unseen during daytime,” he explains. “Even if we have barn cats, if the mice are in the walls the cats can’t get to them.”


Traps and rodenticides may be helpful in reducing numbers, but Timm says, “One of the keys to preventing large infestations is to eliminate shelter.” 

This includes keeping weeds and tall grass away from buildings so rodents don’t have protection from predators as they go in and out of the building. If they have to cross open space to get there, they are more vulnerable to predators.

“Often mice and rats travel at night and depend more on touch and feel with whiskers rather than eyesight. They tend to travel where the ground meets the exterior of the feed bunk, building or barn,” Timm comments. 

“House mice can slip under a door or into a wall if there’s more than a quarter-inch gap. It’s hard to keep mice out because they can go through very small spaces,” says Timm. “Young rats can squeeze through a one-half-inch gap, and both rats and mice can enlarge existing gaps or holes by gnawing.” 

These rodents can even gnaw through softer metals such as aluminum and copper flashing, so exclusion requires using heavier materials such as galvanized steel flashing or galvanized hardware cloth of one-quarter-inch or one-half-inch mesh size.”

Old buildings

Older wooden buildings are more readily invaded. 

“Even with some of the newer materials, the person doing the design and construction may not think about rodent proofing. There are often flaws in a building from the beginning that might allow these creatures to get into walls or attic spaces,” he explains.


Rodenticides can work, and many people use them successfully. 

“However, retail rat and mouse baits have become increasingly restricted in recent years, so in some states users may need to have appropriate applicator training and certification to buy and apply the products,” Timm describes. “In cities, we often see warehouses, restaurants, grocery stores with rodent bait boxes located at the bottom of exterior walls.”

“These boxes may be disguised, but professional pest control companies are maintaining rodenticide baits in those,” he says.

If a farmer or rancher has a continual problem with rodents and buildings that are difficult to rodent-proof, a maintenance program of keeping rodenticides continually present in bait stations – available to rats and mice – can help knock down and hold down the population. 

“The trick is to provide them with something they like to eat better, which is located more conveniently than their other food choices. But be careful we don’t allow access to baits by non-target wildlife, cats, dogs or livestock,” Timm says.

Insulated structures

Regarding house mice damage to insulated structures, often ranchers don’t see the damage until it has already happened. 

“In trials we conducted in Nebraska in the 1980s, we didn’t find any type of building insulation that was mouse-resistant. Mice removed insulation from within walls for nesting materials and made tunnels through it,” Timm explains. “If there was a sheet of Styrofoam sandwiched inside concrete, mice would go in there and hollow out the insulation. This radically changed the energy conservation qualities of a building in just a few years. The solution is to not let them get in, in the first place.”

Many places in North America are cold enough in winter they don’t have house mice living outdoors year-round. 

“They try to find a place to come indoors in the fall,” he says.

Heather Smith Thomas is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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