Black Carpet Beetles, Attagenus spp.

Among the more common household pests you are likely to encounter are the Black Carpet Beetles in the genus Attagenus, family Dermestidae. They are slightly larger, more oval, and jet black compared to the usually more abundant Anthrenus carpet beetles, but they share similar feeding habits.

Adult Black Carpet Beetle

There are nine species of Attagenus known from north of Mexico. Most are about 3-5 millimeters in length as adults. The larvae are distinctive in being tapered from front to back, with a bundle of long hairs extending from the rear end. At maturity the larva is about 9.5-12.7 millimeters, excluding the "tail" of hairs.

Larva of Black Carpet Beetle

As is the case with other carpet beetle larvae, the hairs can cause dermatitis in some people. The patient may frequently interpret the symptoms as insect "bites," resulting in misdiagnosis by physicians. It usually takes years of exposure to carpet beetle infestations to begin exhibiting reactions, but in rare instances, inflammation of the respiratory tract and eyes can also occur.

While the larvae feed mostly on dried animal products such as shed hair and skin cells from people and pets, wool garments and blankets, silks, furs, animal hides, and dead insects that collect in spider webs, light fixtures, and along window sills, they also consume dried plant matter on occasion, especially cereals and grains. So, they can be a pantry pest as well as a clothes closet pest.

Adult Attagenus feed on flower pollen

Control and prevention of a Black Carpet Beetle infestation is best achieved by thorough cleaning of one's domicile, through vacuuming up accumulated pet hair, and dust (most of which is flakes of dead skin from people and pets). Discard any infested items. Outdoors, remove abandoned mammal, bird, and wasp nests. Understand that despite all your efforts, it is next to impossible to become immune to the occasional infestation.

Insects are incredibly adept at exploiting human behavior and household ecosystems. Few are as efficient as Black Carpet Beetles when it comes to scavenging our food and clothing. They are to be despised, no doubt, but also admired for their adaptability.

Sources: Evans, Arthur V. 2014. Beetles of Eastern North America. Princeton, NJ: Princeton University Press. 560 pp.
Gahlhoff, Jerry G., Jr. 2013. "Black Carpet Beetle," Featured Creatures. Entomology and Nematology, University of Florida/Institute of Food and Agricultural Sciences. Publication Number EENY-18. Note the image of the adult beetle depicts a Dermestes species, not Attagenus.
Jacobs, Steve. 2010. "Carpet Beetle Dermatitis," Insect Advice from Extension. College of Agricultural Sciences, Pennsylvania State University.
White, Richard E. 1983. A Field Guide to the Beetles of North America (Peterson Field Guides). Boston: Houghton Mifflin Company. 368 pp.

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.

Larder Beetle

Thanksgiving is an American holiday where we share a big meal with family and friends. Chances are, you might be sharing the leftovers with the Larder Beetle, Dermestes lardarius, as well.

Larder Beetles are members of the family Dermestidae, collectively known as skin beetles and carpet beetles. They feed as larvae and adults on all manner of dried animal products, the larger species enjoying cured meats, dry pet food, furs, taxidermy mounts, even cheeses. Their alias of “Bacon Beetle” gives a clue as to their food preferences. They can also be attracted to the carcasses of dead rodents between walls; or even accumulations of dead insects in light fixtures. I found this Larder Beetle larva crawling out from under our dog’s food bowl earlier this month, probably looking for a place to pupate.

Larvae of Dermestes lardarius average about 12-13 millimeters in length just prior to pupation. They are covered in long hairs like most dermestid larvae, but are distinguished by the pair of hook-like spines on the rear end.

Under optimal conditions, the life cycle from egg to adult can be completed in 40-50 days, but more commonly there is one generation per year. Eggs hatch in an average of less than twelve days after being laid in clutches of 6-8 by the female beetle in a food source. Larvae that eventually become adult male beetles undergo five molts, while female beetles pass through six molts in the larval stage. The insects may spend anywhere from 35-80 days as larvae, probably depending on how easy it is to secure enough food to complete the transition to adulthood. Larvae may wander in search of new food sources, too.

The pupa is enclosed in the last shed larval exoskeleton (“skin”). The larva bores into soft, but relatively solid material such as cork before pupating. The adult insect emerges in about fifteen days.

Adult Larder Beetles are 7-9 millimeters long, and blackish with a broad yellowish band across the elytra (wing covers) as shown. They can fly well. Note the relatively short, clubbed antennae that help distinguish them from other household insects and many other beetles. Adults can be long-lived, sometimes persisting for a year-and-a-half under ideal conditions. The species overwinters in the adult stage, too.

Prior to the age of refrigeration, the Larder Beetle and its cousins were serious competitors for stored food. Today, they are more of a nuisance pest. Prevention is the best way to control them. Store your vulnerable foodstuffs (including dry pet food) in durable plastic, glass, or metal containers with tight-fitting lids. Store furs, wool blankets and garments, and other fibers of animal origin in a cedar chest. Cedar has proven repellent qualities and is quite effective. Forget mothballs (utterly useless) and moth crystals (at least potentially carcinogenic).

I personally find these to be handsome beetles; and I admire their adaptability to exploit our own weaknesses in protecting resources we think are rightfully ours. In this season of giving, sometimes we give by accident. Happy holidays, everyone.

Sources: Bennett, Stuart M. 2003. “Dermestes lardarius (Bacon or Larder Beetle),” Stored Product Insects.
IPM.WG. 2012. ”Larder Beetle,” Museum Pests. Integrated Pest Management Working Group.
Klass, Carolyn. 2011. “Larder Beetle,” Horticulture Diagnostic Laboratory. Cornell University, Cooperative Extension of Suffolk County.

Merchant Grain Beetle

Even entomologists are not immune to pest insects in their homes. We are just a little more fascinated than we are revolted. So, when I found a tiny beetle crawling on the bathroom counter of my Tucson apartment on October 20, 2010, I naturally wanted to know more about it. I thought I had a good idea of its identity, but I was wrong about the species.

Among the more common “stored product pests” found in the average household are silvanid bark beetles in the family Silvanidae. I know! What would a bark beetle be doing in the pantry? Well, while most species live under bark on trees, logs and stumps, other species are pests of stored grains. They are tiny, prolific, and hitchhiking on commerce to all corners of the globe.

The specimens in the images here are about three millimeters long. I thought they were the species Oryzaephilus surinamensis, the “Sawtooth Grain Beetle.” The common name comes from the tooth-like projections on the insect’s pronotum (top part of the thorax). It turns out there is a nearly identical species, the “Merchant Grain Beetle,” Oryzaephilus mercator, and if I am correct, that is what my specimens are. The Merchant Grain Beetle has slightly larger eyes than its counterpart, such that there is scarcely a “cheek” behind each eye. The Sawtooth Grain Beetle has much more prominent cheeks.

Adults and larvae of the Merchant Grain Beetle occur mostly in cereal grains like oatmeal, rolled oats, and bran, and also brown rice. Great, they get more fiber than I do. Oilseed products like nuts and shelled sunflower seeds are also prone to infestations. At optimal temperatures and humidity, these insects can go from egg to adult in three to four weeks.

Adult Merchant Grain Beetles can live a surprisingly long time. Their average lifespan is six to ten months, but they are known to live as long as three years. They are strong fliers, too, which allows them to wing their way to new food sources and locations instead of relying on human transport to exotic new locales (the Sawtooth Grain Beetle is flightless). Females of both species deposit between forty and 285 eggs in their lifetime.

I still don’t know where my beetles are coming from (I found a second one on December 20), and I’m kind of afraid to look. Thankfully, they don’t pose any outright threat to human health. I suppose you won’t want to come over for breakfast now, though….

Sources: A great resource for images of stored product pests in general is the website of the Stored Product Insect Research Unit of the United States Department of Agriculture’s Agricultural Research Service. The entomology departments of many universities produce very helpful online fact sheets about various insects through the Cooperative Extension Service. I found this one from Penn State in my research for this blog entry.