Forensics’ next tool: Hair-collecting caterpillars

Clothes moth larvae pick up tresses from human corpses to make shelters

RENO, Nev. — Clothes moths will eat more than our wardrobe. Given a chance, they’ll eat us too.

CASE CRACKER A caterpillar of the casemaking clothes moth crawls around partly surrounded by its long, lumpy case. Now entomologists have found a caterpillar case (not this one) that incorporated hair from an abandoned human body, a new kind of clue for forensics. Clemson University/USDA Cooperative Extension Slide Series, Bugwood.org

Casemaking clothes moth caterpillars can digest human hair and will feed on corpses. But it’s not all bad news, scientists say.

Hair bits nipped off of corpses by caterpillars of the casemaking clothes moth, Tinea pellionella, can yield enough DNA to identify the deceased, according to entomologist Sibyl Bucheli of Sam Houston State University in Huntsville, Texas.

Particularly helpful is the caterpillars’ habit of retreating to nearby, out-of-the-way corners when it’s time to stop feeding and metamorphose into small tan moths, Bucheli reported November 16 in Reno, Nev., at the annual meeting of the Entomological Society of America. The human body they’ve been feeding on may get moved away, but left-behind caterpillar cases containing human hair can still tie the body to the location, she said.

Casemaking clothes moths rank among the two major wardrobe attackers in North America, though the species remains more of a rural dweller than an urban one.

Scientists have discovered clothes moths nibbling on a corpse before, according to Bucheli. And clothes moth larvae in the wild will graze on a dead animal. “They had to eat something before people invented wool sweaters,” she said.

What’s new is the human hair in the home of the casemaking clothes moth caterpillar. This species takes its common name from the half-inch long, skinny, fiber-fuzzed cases that young larvae build.

Youngsters create the case with one end open, nestle inside and then crawl around in search of food. They feed by sticking out their front ends partway, like chilly campers refusing to climb all the way out of warm sleeping bags. As the caterpillars grow, they enlarge their cases, incorporating bits of nearby fibers into their portable homes.

Bucheli and her colleagues discovered human hair in caterpillar cases when a forensics team asked for help with an abandoned body discovered in August 2007 in a Galveston County, Texas house. Witnesses who had hung around the house in the past said they hadn’t seen the deceased for more than a year, since the previous summer. Investigators asked Bucheli whether the insects around the body offered any clues to when the person had died.

Investigators presented Bucheli with what she describes as “basically a salad crisper” full of hundreds of insects, dead and alive. Among them were the clothes moth larvae in their cases still feeding on clumps of the deceased’s hair. The parts of the cases made most recently bristled with stubs of human hair.

The hair shafts yielded enough mitochondrial DNA for Bucheli and her lab to sequence a repetitive bit of genetic material commonly used for forensic identification.

To determine the timing, Bucheli and her colleagues relied on the insect assemblage, which lacked some of the flies and other species that routinely visit fresh corpses in warm weather. Thus, the person probably had died during cool weather, not in summer as the witnesses had claimed, she concluded.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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