Tuesday, March 15, 2016

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.  

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