Don't
be a Victim of Larder Beetles
You go to your pantry to get some dry food for your pet. As you reach for it, you notice a couple of small, dark, hairy-looking "worms" on the bag. When you look closer, you see a couple more on the shelf, away from the bag. There are even several small holes in the wooden molding along the edge of the shelf. In that case, you are probably the victim of Larder Beetles.
Larder beetles are cosmopolitan stored product pests which infest high-protein, animal materials, such as hides, meats, cheese, feathers, or hair. They often infest dried pet foods, fish, or nearly any product of animal origin (frequently found in pantries). They very rarely eat materials of plant origin. They may invade museum specimens, dead insects, or accumulated lint and hair in wall voids.
Adult Larder Beetles are 1/4 - 3/8 in. long, oval beetles, with a pale yellow band across their back which is about 1/3 of their total length. Both the front one-third and the back one-third of their body is dark brown to black, and there are 6 to 8 dark spots on the yellow cross-band. Their antennae are short, clubbed, and fit into grooves under their pronotum. Their head has no median ocellus (simple eye). Larvae are 3/8 - 5/8 in. long dark brown and covered by dark brown hairs (setae). These often appear to be arranged in bands across their body, alternating with lighter inter-segmental bands. They have a pair of backward directed, pointed, projections (called urogomphi) which are sharply curved backward and downward in side view.
Adult females lay 100-800 eggs on suitable larval food, or in cracks near where such materials are stored or have accumulated. Usually, male larvae molt five times and female larvae molt six times. Then they crawl away from the larval food, find a suitable site and pupate. A complete life cycle takes 2-3 months. In temperate climates, there is only one generation a year, but as many as six generations a year have been reported under optimal conditions overwintering in crevices in tree bark, or similar sheltered sites. Then they enter buildings in the Spring seeking sources of larval food. Adults live about 3-5 months in warm (Summer) conditions. Adults avoid light during mating and when laying their eggs.
Most damage is done by larval feeding. When larvae are mature, they may crawl several feet away from the material they were feeding in, and drill a hole up to 1/2 inch deep in soft wood. They have even penetrated up to 1/16 inch thick sheets of soft metals such as copper, aluminum or lead. They may even penetrate thin plastic. A plastic bag of at least 3 mils thickness may keep adults from detecting its contents, even if those were items they would normally infest.
The key to controlling Larder Beetles is to find all their breeding sites and eliminate them. Start by examining dry pet foods and pantry areas nearest where you first discovered the beetles, but be sure to consider furs, animal hides, hunting trophies (often mounted and hung on a wall), and decorations or wall hangings made from or containing skins, hair, or leather. Also consider past problems with flies, ladybugs, rodents or birds. This inspection should be followed by good sanitation (removal of all infested materials found), and application of a properly-labeled pesticide when needed.