Carpet Beetles, Genus Anthrenus

As a volunteer answer-man for AllExperts.com, I receive many questions pertaining to carpet beetles, tiny coleopterans in the family Dermestidae. In fact, I venture to say that at least seventy percent of the queries I get are related to carpet beetles and their larvae. Ironically, I now live in a region where these beetles are relatively scarce.

Anthrenus sp. larva, Colorado

Yesterday, I finally found a living larva of the most troublesome genus most people find: Anthrenus. The hairy grub was only about four millimeters in length, and crawling up the bathroom wall. This is an unfortunate commentary on our housekeeping habits, I suppose, but even the cleanest homes will have carpet beetles at one time or another. It takes precious little to feed them.

Carpet beetle larvae eat all manner of dried animal products, especially the shed hair and skin cells of pets and people. This food supply accumulates faster than you might imagine and, despite vacuuming regularly, can persist in out-of-the-way corners and beneath furniture.

Additional items on the carpet beetle menu include wool blankets and garments, furs (but you don't have animal hides, right?), taxidermy mounts, dry pet food, and insect collections (including my own, horror of horrors!).

Adult Anthrenus lepidus, Colorado

Getting rid of an infestation of dermestids is a real challenge. Traditional methods are of questionable effect. One of my good friends in entomology and pest control, Bill Warner, has found that moth balls, which have the active ingredient of naphthalene, are not just useless. He has observed carpet beetle larvae eating the substance. Ok, so what about moth crystals, with the active ingredient PDB (paradichlorobenzene)? At high enough concentration, that seems to work, and I have used moth crystals to protect my own insect collection. Unfortunately, PDB is potentially carcinogenic, according to the World Health Organization. The U.S. Environmental Protection Agency claims it is "not likely to be carcinogenic to humans" (National Pesticide Information Center website).

The best course of action when faced with numerous carpet beetle larvae is to discard the infested item. If you cannot bear to part with whatever is under attack, then a cycle of freezing and thawing over the course of several weeks may do the trick. This is how most museums now handle pest control in their entomology collections.

Prevention is the best cure for dermestids. Store vulnerable foodstuffs, like dried meats and dry pet food, in metal, glass, or durable plastic containers with tight-fitting lids. Store woolens, silks, and furs in a cedar chest when not in use. Cedar has proven repellent qualities and is not toxic to people or pets. Vacuum and clean your home regularly.

Adult Anthrenus sp., Massachusetts

Adult carpet beetles are pretty tiny (2-4 mm), and frequently mistaken for lady beetles since they are round, and often patterned with bands or spots of brown, black, and white. The beetles fly well and seek escape to the outdoors. Consequently, they are most often observed on windowsills, or discovered in light fixtures.

While carpet beetle larvae are pretty much "juvenile delinquents," the adult beetles can be surprisingly efficient pollinators of some flowers, especially in spring. The Buffalo Carpet Beetle, Anthrenus scrophulariae, is particularly common in flowers.

Larva of Anthrenus verbasci, © Canada Dept. of Agriculture

Carpet beetle larvae are covered in tiny hairs called setae, and these hairs can break off and become airborne, especially from the molts (shed "skins") of the larvae. These setae can cause irritation, or even trigger rhinitis or asthma in people prone to allergic reactions. Contact dermatitis is a more uncommon reaction, and an infestation has to be pretty severe to result in any kind of medical consequences (Peacock, 1993).

There are eighteen (18) species in the genus Anthrenus currently recognized in North America, and several of those are cosmopolitan pests now found worldwide as a result of international commerce. There are other common types of carpet beetles as well, with the genera Trogoderma and Attagenus being common in households. I will address those in separate blog posts.

Sources: Boone, Mike. 2013. "Genus Anthrenus - Carpet Beetles," Bugguide.net.
Gibson, Arthur and C.R. Twinn. 1931. Household Insects and Their Control. Ottawa: Department of Agriculture, Canada. 87 pp.
National Pesticide Information Center.
Peacock, Enid R. 1993. Adults and Larvae of Hide, Larder, and Carpet Beetles and Their Relatives (Coleoptera: Dermestidae) and of Derodontid Beetles (Coleoptera: Derodontidae). London: Royal Entomological Society of London. Handbooks for the Identification of British Insects, vol. 5, part 3. 84 pp.