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In the city of Mashhad in northeast Iran, there's a natural history museum associated with local Ferdowsi University that gets all manner of donations, including animals that died in the road and injured birds.
With all these specimens pouring in, the research team quickly ran out of space.
"We don't have enough freezers to put these dead animals," says Niloofar Alaei Kakhki, a bioinformatician who's studied and worked there. "We have to find a way to clean them," she adds, so that these animals' skeletons can be studied and exhibited.
Researchers use a range of techniques to strip the flesh off an organism, but each has its drawbacks. In a paper published this month in PLOS One, Alaei and her colleagues propose an alternative — employing a suite of superworms, a kind of hefty beetle larva that can capably pick a variety of animal skeletons clean.
The worms work fast, yet they're "super gentle," says Alaei.
Introducing the superworm
Among the existing methods for cleaning flesh off a specimen is chemical treatment, but that tends to be bad for the environment and can degrade the skeleton. Another option is boiling, but it's time-consuming and can damage "tiny, delicate bones," says Alaei.
Then there's the use of another kind of insect, dermestid beetles, which quickly chew away the flesh, but if they escape, "it could be really dangerous for the museum collection," she says. That's because they're likely to destroy preserved specimens by chewing through feathers and dried skin.
Then, some years ago, Alaei's colleagues in Iran turned their attention to Zophobas morio — the superworm, which is native to South and Central America. Each one is nearly the size of a human finger, they have large chewing mandibles, and they're available as feed at many pet stores. Superworms are usually devoured by other animals, but Alaei says she and her colleagues wondered: What if they did the eating instead, chewing up flesh to clean valuable specimens?
Superworms transform into adult beetles only when they're isolated, explains Alaei. So as long as they're kept together, they're essentially locked in their larval state, unable to wreak havoc elsewhere in the museum.
"You can reuse the same larvae for almost six months," she says.
Superb skeletal sweepers
Alaei and her colleagues exposed superworms to dead animals of all sizes, ranging from mice, fish and small birds to wolves and wild cats. They pre-cleaned the specimens slightly, softened them in hot water for a few minutes, and then let the superworms have at them.
Alaei says they did a remarkable job with no apparent side effects, even cleaning "the ribs of the fish, which is super, super tiny."
To clean a specimen, the researchers found that 10 to 15 larvae work best. It's the right number to move things along at a reasonable clip without damaging the fragile bones.
Alaei, who's now based at the State Museum of Natural History in Stuttgart, Germany, hopes the superworm's success with cleaning skeletons, combined with their commercial availability, could be good news for all kinds of institutions, even small ones with less advanced facilities.
"This study is adding one more possibility when you need to clean something," says Damien Charabidze, a forensic entomologist at the University of Lille in France who wasn't involved in the research.
He says that superworms may well be easier to control than dermestid beetles, but he worries that the superworms' powerful mandibles could inadvertently snap a small bone. Plus, although they're omnivores, they prefer a vegetarian diet. So cadavers, he explains, are "not their usual food," and that could make them more finicky feeders.
Marna Sakalem, an anatomist at the State University of Londrina in Brazil who didn't contribute to the research, raised a similar concern. And she adds that in the five years that she's worked with dermestid beetles, she and her team have not observed any escapees — so she's not willing to write off more traditional approaches just yet.
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