Dermestid beetles (family Dermestidae) can either be a useful ally or a nuisance, depending on your point of view. There are several hundred species worldwide, and many have found ways to either enrich or aggravate our lives.
If you are interested in taxidermy or specimen preparation, these industrious beetles are one of the best ways to de-flesh and clean skeletons. Entire colonies are kept by hobbyists, universities and museum collections and put to use, both adults and larvae feasting on an array of carcasses. They especially enjoy hair, skin, and feathers.
Due to their knack for feeding on dead or decaying materials, they are essential outdoor decomposers. Some species prefer plants, some prefer animals, and some get rather esoteric in their choices (like specializing on praying mantis egg cases). Our knowledge of these ecosystem services also allows us to use them in forensic investigations.
But most people don’t think of these applications. They are more concerned with the “larder beetles” in their pantry, pouring out along with the cheerios into their cereal bowl. Or “carpet beetles” munching on wool coats, or silk scarves, and other natural fibers in their closet. Any open window is an invitation for a visit.
And if you’re an entomologist, the phrase “dermestid beetle” should strike fear into your heart. All the qualities that make these beetles desirable for cleaning vertebrate skeletons makes them especially destructive if let loose in an insect specimen collection. These beetles don’t just like the taste of skin and fur, they have quite a fondness for insect chitin and dried innards.
Every entomologist I know has horror stories of dermestid beetles infesting their collection. The main specimen collections here at UConn are chemical-free, meaning they have strict quarantine procedures in order to thwart these beetles and other pests. Specimen boxes must be frozen twice, if they’re allowed inside at all.
I was cleaning out a storage room for the entomology teaching lab, and came across a set of student specimen boxes. That had been overlooked since 1994. Needless to say, dermestid beetles had a feast. The boxes were absolutely filled with insect bits and old dermestid skins. Just about all of the specimens are ruined, and will be thrown away.
So, what should you do? In your home, make sure all food containers are tightly sealed and secured (anything that comes in a bag, I transfer to a jar). Store winter sweaters and other important clothes in sealed containers or plastic bags. Ensure all household screens are tightly fitting with no gaps.
For an insect collection, you can choose to use chemicals like mothballs, but they wear off after a while (I have personally observed collections with chemicals tacked into one corner… still filled with dermestid damage. See the first image above.) Your best bet is to keep the collection sealed in a tight wooden box or glass topped drawer. Cardboard boxes, such as we give students, should be temporary. When in doubt, if a collection will not be regularly used, keep the box(es) in a sealed plastic bag of some sort. Also keep workroom/lab windows closed, or ensure screens are tightly fitting. My advisor likes to say “dermestids smell insect specimens the way you smell Starbucks!” Which may or may not be true. Probably true.