Do carpet beetles "sting"?

Varied carpet beetle larva.  The tufts of hair on the final tail
segments (right) are barbed and have been associated
with dermatitis and gastrointestinal upset in some people.

Dermestid beetles (Coleoptera: Dermestidae) are among the most common indoor pests throughout the United States.  The principal damage caused by these beetles occurs when they feed on stored products containing animal protein, such as woolen sweaters, rugs, silks, furs and feathers.  Also products containing dried dairy and grain based foods may be attacked. Outdoors, dermestid beetles may feed on dead animals or may scavenge in bird and other animal nests.

What's less known about these beetles is that they occasionally make people sick. I was reminded of this today after being asked whether carpet beetles could bite from two email correspondents.  Now it's true that carpet beetles do not bite, but they can affect people in other ways.

Small hairs called hastisetae are found on the larvae of some dermestid beetles, especially in the genera Anthrenus (carpet beetles) and Trogoderma (warehouse beetles).  These hairs can cause urticaria, dermatitis, vasculitis, lymphadenopathy, and allergic rhinitis in sensitive persons, as illustrated by a recent paper in Pediatric Dermatology from Kara Hoverson and colleagues.

Multiple beetle-caused, excoriated lesions on the
face of a 2-year-old girl. From Hoverson et. al. 2015.

In this paper a two-year old girl experienced skin eruptions on her feet, face and hands.  Subsequently, a few carpet beetles were found in the patient's stuffed animals, mattresses, drawers, baseboards and nightstands, according to the article.  Pesticide applications alone were ineffective in stopping the lesions; but after thorough vacuuming, carpet steam cleaning, and discarding of old bedding and linens, along with physician prescribed ointment treatments, the lesions improved by 70%-80%.  By two weeks after treatment, all lesions were healing. The mother had only a few lesions and the father, who traveled extensively, had none.

An adjoining apartment was found to be even more heavily infested, possibly the original source of the problem.  Occupants of that unit were not bothered by the beetles and refused treatment. Dermestid beetles found in the apartment included larder beetles (Dermestes lardarius), beetles in the genus Anthrenus (carpet beetles) and the genus Attagenus (furniture beetles).

Such hypersensitive reactions are not new to the medical literature.  The Pennsylvania State University published a fact sheet on carpet beetle dermatitis that summarizes reports from 1948 concerning several case histories.  In addition, carpet beetle larvae can cause gastrointestinal upset if swallowed, for example in infested milk, cereal or grain products.

All this does not make carpet beetles an especially alarming indoor pest. Dermestid beetles are very common in homes, especially in the South.  Yet, reports of hypersensitive reactions to contact with carpet beetles are rare in the medical literature. Even when beetles are present in a home, direct contact with humans is not common. And finding a few carpet beetles in a home does not necessarily mean that they are automatically the cause of skin lesions.  Nevertheless, customer reports of "bites" or lesions should be investigated when carpet beetles are apparent.

Complicating matters further, carpet beetles are, not surprisingly, often collected from apartments of people with suspected delusions of parasitosis. This can make diagnosis of such a condition more difficult, because it may require ruling out beetle-related dermatitis as a cause of suspected bites or skin irritation.

Delusions of parasitosis, however, normally involve unreasonably high levels of stress and irrational response to perceived pest problems, beyond what would be considered a normal response to a minor or undetectable pest infestation. PMPs who encounter mystery bug cases where carpet beetles are present, should recommend a thorough (HEPA) vacuuming of furniture and other likely sources of infestation, including cleaning of bed linens.  In addition a thorough inspection should be made for possible sources of a beetle infestation, including use of sticky traps.

I have carpet beetles in my home, but this information will not change the way I view these persistent insects. When I see a carpet beetle my first concern is for any expensive sweaters stored in our closets.  Good housekeeping will keep most carpet beetle populations at acceptably low levels in most homes.  

Anthrenus verbasci: the "adaptable" carpet beetle

One of the relatively common household pests that sometimes puzzles PMPs is the varied carpet beetle, Anthrenus verbasci.  The 3 mm-long adult is easy enough to recognize under magnification with its colorful zig-zag banding of white, black and orange scales.  The larvae are less commonly seen, but equally distinctive.  Cigar-shaped and hairy, they are often described by PMPs as banded, but close inspection reveals the banding to be the result of the darker colored dorsal plates contrasting with the lighter base color of the insect's body.

Varied carpet beetles might be better named the "adaptable carpet beetle" due to their catholic tastes in food. They differ in their eating habits from other beetles in the family Dermestidae, which normally require animal-derived proteins in their diet to survive and reproduce.  Examples of such other dermestid beetles include the black carpet beetle, the hide beetles, and the warehouse beetles.  The preferred foods of most dermestids include natural furs, feathers, wool, silk, dried milk and meats, taxidermy mounts and hides, dog food (with meat ingredients), dead insects, etc.  The varied carpet beetle readily feeds on these items, but can also subsist on a plant-based diet, such as drugs, spices, flour, nuts, wheat, corn, cereals and seeds.  Or, as I learned last night, the cheese crackers under my daughter's bed.

My youngest daughter is a Junior in college, and to judge from the archeological strata under her bed, the box of crackers probably dated from high school.  The discovery was prompted when my wife asked me what the two little larvae were under some books on our daughter's bed.  They turned out to be carpet beetle larvae, and the fact that there was more than one prompted me to go on a search and destroy mission.  Sure enough, the cracker box was soon located and the source confirmed. 

One thing I like about insects is that they never lie. If an insect is found indoors, there is always a reason.  An occasional carpet beetle may be found indoors after munching on dead insects in a light or windowsill, or from a bird nest or bee hive; but more than one is usually an indication of a problem.

The varied carpet beetle is not a good insect to allow to flourish in a home.  Along with its dermestid cousins, this beetle is one of the most likely culprits responsible for those mysterious holes in your favorite sweater.  As with all stored product insect pests, the best solution is not usually pesticides, but rather a thorough inspection to look for, and remove, likely food sources.  Last night's invasion was a relatively simple problem to solve.  Unfortunately, they are not all that easy.

Most dermestid-infested items are old, forgotten or spilled food in out-of-the-way places, old rodent baits in attics, or furs, feathers or woolens that do not get worn or used frequently. Pet hair tucked into carpet edging, furniture and who knows where, can be another meal for varied carpet beetle and its other dermestid beetle cousins. 

Knowing something about carpet beetle biology and identification can help you solve those tough pest control problems for your residential customers.  Recognizing that you have a varied carpet beetle means you will have to widen your or your customer's search efforts to include both animal and plant-based protein sources.

My daughter's bed has now officially been purged of cracker boxes, dirty socks and high school notes.  Next time she's home from college, you can be sure we will tackle the CLOSET.  Who knows what new life forms we'll discover?