Adults are More Obvious But Larvae are the Problem
Four different species of carpet beetles in the dermestid family can be common pests in homes and other buildings where the larvae feed primarily on materials of animal origin such as hair, hides, woolens, felt, and feathers. Because they also feed occasionally on stored foods, carpet beetle larvae are common in corners, under furniture, and behind baseboards where they happily feed on accumulated pet hair, lint, skin flakes, and miscellaneous household crumbs and debris. Like the hide beetle or the larder beetle (related dermestids), carpet beetles will also infest carcasses, dead insects, and miscellaneous debris in animal, wasp, or bee nests.
It's probably safe to say that most homes have at least a few carpet beetles present and in most cases they are not infesting carpets. Ongoing, low-level infestations usually go unnoticed. The active larvae are only about 1/4 inch (6 mm) long, brown, with rows of bristly hairs and tufts of hair at the rear end. The elusive larvae do all of the feeding damage. Adult beetles are broadly oval, 1/16 to 1/4-inch (1.6 - 6 mm) long and usually seen seasonally.
Signs That You May Be Dealing with Carpet Beetles
Tiny beetles climbing walls or found dead at windowsills - Carpet beetles emerge from pupation and head to windows or lights, looking for a way outside where they gather on flowering plants and eventually mate. Some are not much bigger than a pin head and at first glance, appear dark. But on close examination, the three Anthrenus species (varied, furniture, and common carpet beetles) are calico-colored with brown, white, black, reddish-orange, or yellow markings, while the larger black carpet beetle, Attagenus unicolor, is dark brown to black. Although the adult beetles can fly to light, they are most often noticed crawling up walls or around windows or light fixtures in early spring.
Small holes or bare areas in wool clothes, blankets, wall-hangings, etc. -Carpet beetle larvae eat the nap from the surface of wool or wool-blend fabric, leaving just basal threads, or they may eat irregular holes completely through the fabric. The holes may connect leaving a larger damaged area. Soiled materials, especially those stored without cleaning, are most likely to be infested. Silk and non-animal fabrics, those of plant or synthetic origin, can be attacked if they are soiled.
Thin, bare areas on wool or wool-blend rugs. Because carpet beetle larvae avoid light and feed in hidden, dark areas, they are rarely seen. They can be found on the underside of rugs or carpets or hidden deep within the pile of a rug and may "play dead." When rugs are attached to the floor, larvae eat slits following the cracks below.
Shed larval skins in hidden areas. Carpet beetle larvae molt or shed their skins several times as they grow. The light brown, empty skin casings (exuviae) remain behind and can accumulate in areas where a number of larvae have been feeding. Look for the cast skins on the undersides of rugs, in folds or hidden areas on clothing or wool blankets, or under furniture or in corners where lint, pet hair, and dead insects collect.
Hairs falling out of trophy mounts or furs. When carpet beetle larvae feed on hairs in furs, animal mounts, or bristle bushes, they clip the hairs off at the tips, leaving uneven edges. Clipped hairs or droppings beneath may be the first clue to infestation.
Treatment and Prevention of Carpet Beetles
When you find a number of carpet beetles in various sites, they are usually randomly infesting lint and hair and can be best controlled with vacuuming, paying particular attention to pet hair, crumbs, dead insects, and other debris in hidden locations, including air ducts. Crack and crevice treatment of infested areas can be useful. Dry cleaning will kill carpet beetles; storage of woolens in air-tight containers is important.
If you can't find the source of a serious carpet beetle infestation in living spaces, check the attic above. Carpet beetles may be infesting a hidden rodent or other animal carcass, hoarded food or rodent bait, an abandoned yellowjacket or bee nest in a void, a mouse or bird nest, bat roost, or piles of dead overwintering insects in an attic. When you remove an animal living in a home, or if you eliminate a bird, wasp, or bee nest in a void or attic, it's important to remove the nest remains, clean up, and if necessary, dust or otherwise treat the area. Carpet beetles can move in to feed on anything left behind: hair, feathers, droppings, dead young, hoarded food, dead wasps or bees or their larvae, even beeswax.
You may also have an ongoing infestation in an oriental rug or other woolen item, upholstered furniture, or in a treasured trophy mount on a wall. These items can often be treated with insecticide but you risk staining or damaging the item - test an inconspicuous area first. Chamber fumigation or freezing are other options. Pheromone lures are available for ongoing monitoring of carpet beetles.