Skull being cleaned by dermsetid beetles
Wikimedia Commons

In an underground vault of a mid-century missile bunker, thousands of glistening beetles encrust a pile of decomposing skeletons. An array of still-reddened rib cages and leg bones line a nearby table, baking beneath the light of 60-watt lamps. The scene may sound straight out of a horror film, but this colony of dermestid beetles works in the service of a higher order: the museum collections of Harvard University.

For over a century, the appetite of dermestid beetles—so named for their love of skin—has earned them a small but significant role in the annals of natural history. More recently, the beetles have proven forensically useful for dating, cleaning, and even identifying dead bodies. The insect’s prodigious ability to skeletonize carcasses in a quick, clean, and noncorrosive fashion has kept it the gold standard over a variety of other methods. Burying bodies or soaking them in water gets the job done but takes a long time, while using chemicals like acid or bleach can damage the quality of bones and pose health risks to researchers.

Though flesh-eating beetles make strike you as exotic, chances are you pass colonies of them every time you hop on a highway or country road. Dermestid beetles inhabit every continent except Antarctica, and they can usually be found on decaying remains. They show up to the road-kill buffet about a week after an animal’s death, following one or two waves of other insects that don’t mind eating through fur or feathers.

Of an estimated 600 species of dermestid beetles, only one is used in museums and forensics: Dermestes maculatus, also known as the hide beetle. Adults grow to the size of a puffed rice grain, their shiny black bodies covered in minute yellow hairs. An entomologist wrote in the 1940s that their underside “reminds one of cream-colored velvet.” It’s as voracious larvae, however, that dermestid beetles do the bulk of their bone-cleaning work. The hairy and segmented brown larvae pass through as many as eleven developmental stages, or instars, before metamorphosing into adults—meaning they can be ravenous eaters.

Judy Chupasko, the mammals collection manager at Harvard’s Museum of Comparative Zoology, is one of the people who harnesses the hunger of dermestid beetles in the name of science. Twice a week, Judy descends the stairs of the repurposed Nike missile bunker to tend her beetles. Four porcelain bathtubs propped waist-high on cinder blocks serve as enclosures for the colonies, their lids fitted with fine mesh screens to facilitate airflow. In the base of each tub, a mix of larvae, pupae, and adult beetles swarm metal baking sheets laid with cotton batting and dead animal parts.

The animals come from all over. When mammals at nearby zoos die, when whales or dolphins beach themselves on the New England coast, and when state officials find dead wildlife that might serve research interests—many of the bodies end up on the menu for Harvard’s beetles.

“You get used to the smell,” Chupasko promises, but she and assistant Mark Omura still take steps to reduce its potency. Under the steady warmth of regular light bulbs, the bones and meat dehydrate to prevent mold and rot, which can kill dermestid beetles in addition to reeking. Before carcasses are fed to the beetles, they’re meticulously skinned, debrained, and cut up into smaller chunks. Judy leaves only half an inch of meat on the bones, stripping away the rest to be dried under lamps. The result, Chupakso says, looks pretty similar to beef jerky, and gets thrown in the freezer until the beetles need a snack.

Dermestid beetles are gluttons for fatty substances (a 1956 study found they prefer bones dipped in bacon drippings, second only to cod liver oil), but they’re happy to subsist on exotic jerky and an occasional spray of water.

Every museum manages its beetle colonies with slight variations in practice. At the Denver Museum of Nature and Science, beetles are largely cared for by an inveterate thirty-year volunteer. “We call her the Dermestodian,” writes collections manager Jeff Stephens in an email. “The beetles are kept very well fed, with new food added two times a week, cleaning once a week, and spritzing with water every other day.”

The Denver Museum’s colonies inhabit a variety of glass, plastic, metal, and porcelain containers, and include one small colony that Stephens calls “the king’s tasters.” An animal of unknown origins that arrives at the museum may contain chemicals in its flesh—DDT, for instance—that could kill a decades-old beetle colony. To guard against such a risk, the Denver Museum keeps “the king’s tasters” on hand to test suspect carcasses.

With a little tender care, dermestid colonies can persist indefinitely. Judy’s colonies have been at Harvard at least as long as she has, since 1989. “We’ve never had an infestation of mites,” she says with a hint of pride, so “we’ve never had to wipe them out.” That means dozens of generations of beetles have hatched, grown fat, and metamorphosed under her care. The Denver Museum’s beetles are even older—Jeff Stephens estimates that one of their colonies has been around for over thirty years.

Dermestid beetles serve an invaluable role in preserving animals for future research and education, but they also serve a critical ecological function in the wild by eliminating carrion. Their habits in nature prove most helpful to forensic entomologists, who use clues left by insects to compile evidence in criminal investigations such as homicides.

“The basic science is that insects will show up immediately after death, and they last a certain amount of time,” says forensic entomologist Adrienne Brundage, who teaches at Blinn College in Texas. “We go to the body and we see what insects are left.”

Depending on the temperature, dermestids show up within five to eleven days, after a body has dried out a bit. Because bodies tend to be found either very quickly (when they smell) or after they’ve decomposed, dermestids fall in a time frame that is not always of use to investigators. They offer forensic entomologists another secret weapon, though: their poop, also known as frass.

Dermestid beetle frass possesses the distinction among insects of a membrane that seals out moisture and the elements. Researchers can extract amazing details from the well-preserved frass, including DNA and toxicological information from the body of a victim. Even mummified frass that’s been underground for years has provided useful evidence for cases, Brundage says.

In an age of technological fixes, even old-fashioned disciplines like natural history are looking for ways to bring their collections into the twenty-first century. These little black bugs are holding their own, though, and aren’t likely to be replaced anytime soon. Dermestid beetles continue to prove their importance to science, eating their way through one dead thing at a time.

Tags: dermestid beetles, entomology, forensics