Larder beetles in homes
Larder beetles were named for their attraction to larders where they fed on cured meats. While this situation is not common today, larder beetles can still be found in homes, attacking a variety food sources.
The adult beetles are dark brown and oval shaped. They have a cream to yellow colored band across the top of their wing covers with six dark colored spots inside it. They are about 1/4-1/3 inch in length (fig. 1).
The larvae are worm-like, fairly hairy, reddish to dark brown in color. They have a pair of spines on their tail end that curves backwards. Larvae grow to about 1/2 inch in length (fig. 2).
Adult larder beetles overwinter outdoors as well as indoors in walls. It is common for them to enter homes in spring through spaces and gaps they find around the outside of buildings. They lay eggs in food sources they find for their larvae. Both adults and larvae eat high-protein materials, such as animal hides and furs, feathers, meat, cheese, dry pet foods, and dead insects.
When the larvae are full grown, they wander about, searching for a place to pupate. It is not uncommon for them to bore a short distance, about 1/2 inches, into wood for protection. Larvae may also bore into other soft materials, such as books and insulation.
Larder beetle problems commonly occur when insect infestations, e.g. cluster flies and boxelder bugs, get into homes during late summer and fall as they seek shelter for the winter. When large numbers of them die in wall voids, attics, and similar places, they attract larder beetles to that area the following year. Larder beetles can also feed on animal carcasses, such as mice or squirrels that become trapped inside buildings and die. Often items hidden by rodents may also provide food for these beetles.
Larder beetles can potentially infest certain types of stored food products, although this is not commonly seen. They can infest dry pet food and render it inedible. Larder beetles can be potentially destructive to preserved animal specimens. When larder beetles infest dead insects, animals or birds in voids or attics, they are primarily considered as nuisances.
When larvae are found boring into wood, the damage is usually not serious. It is possible in extreme cases for the wood to be structurally damaged when larvae repeatedly bore into and pupate in it.
The presence of a few adult larder beetles does not necessarily mean there is an infestation, especially if they are found during spring. They may have simply come in from the outdoors and may not be associated with a food source. Physically remove and discard any larder beetles that are found. However, if you are continually finding larvae or large numbers of adults, this indicates an infestation is present.
When an infestation is present, the first step in larder beetle management is to try to determine the source of this infestation and remove it. Look in areas where you see the most larder beetles and particularly check out areas where food is stored, including dry pet food. In some cases, e.g. a small spill of dry pet food, the source of the problem may be fairly obvious and easy to clean up. However, in other cases, the source may not be as easy to detect and you may need to become a detective to locate the source of the infestation. You may require an inspection of your home for rodent activity, especially if your home or cabin has a crawl space.
If the food source is suspected to be dead insects or dead animals in the walls or somewhere inaccessible, then control is more challenging. As long as a food source remains, larder beetles will continue to be a problem. Your best option is to physically remove larder beetles (e.g. with a vacuum) as you see them. Insecticide sprays or dusts applied indoors will have little lasting effect on larder beetles as long as a food source is available.
You can reduce the number of overwintering insects by treating them in the fall before they get inside. Their management is a two-step process. First, seal cracks and spaces around your home that may allow insects to enter. Second, apply a residual insecticide around the exterior of your building. These insecticides must be seasonally timed to provide protection before the overwintering insects become a major problem. A reputable pest control service can also be hired to treat a home for overwintering insects. For more detailed information on controlling overwintering insects, see the specific fact sheet of the insect you are dealing with: http://www.extension.umn.edu/garden/insects/find/insects-by-category/#household.