The Flesh-Eating Beetles that Work at Natural History Museums

Not long ago, the thing in the tank was a living animal—a bobcat that prowled and hunted the way bobcats do, and then eventually died. What’s in the tank doesn’t resemble a bobcat, though. It’s just a mass that looks a little bit like jerky meat still on the bone. And the bobcat isn't alone, either: Little black beetles and setae-studded larvae are swarming all over the meat, devouring it. Put an ear to the top of the tank, and you’ll hear something akin to the snap-crackle-pop of Rice Krispies just drenched in milk—the sound of thousands of dermestid beetles hard at work.

The bobcat is on its way to becoming an osteological specimen at Chicago’s Field Museum. Like most natural history museums around the world, the Field uses Dermestes maculatus, or hide beetles, to clean its specimens. The museum has 10 colonies, which live and work in aquaria around a third-floor room that’s closed off from the rest of the museum by two double doors. The specimens within the tanks are in various stages of cleanliness: One holds what appears to be a sloth arm, and in some, beetles and larvae hunt for meat on skeletons that are nearly picked clean.

Across the room, on a countertop next to the sink, carcasses stripped of their skin and excess musculature sit drying on racks and plastic trays. “The beetles like the meat a little bit dry,” explains research assistant Joshua Engel. He points to one—“this is a seagull”—then another: “This one might be beaver.” The scent of putrid meat hangs in the air. “You get used to it pretty quickly,” he says.

If the thought of beetles eating the meat off animal bones in an enclosed space turns your stomach, you’re not alone. But despite the ick factor, natural history museums are so indebted to the insects that they’ve been nicknamed “museum bugs.” And in fact, dermestid beetles have a number of advantages over other osteological prep methods: They eat the tissue from specimens in a fraction of the time (a colony can clean off a small rodent in just a few hours, a big bird like a seagull in a few days), are significantly less messy than other methods, and are much less harmful to the bones themselves. “We love them,” William Stanley, director of the Field Museum’s Gantz Family Collections Center, tells mental_floss. Dermestid beetles are, he says, the unsung heroes of natural history museums. As long as they don’t escape.

D. maculatus larva. Photo by John Hallmén. Embed via Flickr.

 
There are many, many species in the Dermestidae family, and if you look closely enough, you can find them anywhere. Have you spotted carpet beetles under your rugs, or Khapra beetles in your pantry? Congratulations—you’ve met a dermestid.

D. maculatus (which has also gone by the name D. vulpinus) can be found around the world. According to scientists at the American Museum of Natural History, the beetles go through a complete metamorphosis: egg, larva, pupa, and, finally, adult. The eggs, which are about a millimeter in size, hatch around three days after they’re laid. Then comes the larval stage, during which the larvae go through seven or eight instars. With each molt, the beetle-to-be sheds its exoskeleton.

It’s at this stage that a beetle is the most efficient. Though both the adults and the larvae eat, “the larvae are doing most of the cleaning,” says Theresa Barclay, manager of the dermestid colonies at the Museum of Vertebrate Zoology (MVZ) at Berkeley. “By the time they become adults, they’re not eating as much.” The more larvae are present in a colony, the faster specimens get cleaned.

When it’s time to pupate, the larva does so in its own skin—no cocoon here. The adult beetle emerges after five days, goes through five days of maturation, and then becomes reproductive, mating and eating for the next two months. (Females can lay between 198 and 845 eggs in that time.) Then they die, joining the ever-growing pile of frass—old exoskeletons ground to dust, beetle poop, and dead insects—at the bottom of the tank.

A single beetle’s lifespan is about six months, but depending on the size of the tank, the life of a museum colony can be much longer. According to Stanley, the Field Museum’s colonies last for about five years—and that’s a limit only because the tanks fill with frass and need to be cleaned out. “It takes literally years for that dust to build up until it’s so high that we can’t fit any more skeletons into the aquarium,” Stanley says. “So we stop giving that aquarium any food, and slowly but surely, the colony dies off.” After freezing the colony for seven days to make sure the bugs are good and dead, the whole thing goes in the trash (frass doesn’t make good compost). “Then we have an empty aquarium,” Stanley says, “and we start all over again.”

But that all makes the process sound a little too easy. Getting the beetles to chow down just the way a museum director needs them to has taken decades of work—and some people didn’t even want them in museums in the first place.

 
There’s no precise record for when naturalists decided to put dermestid beetles to work in museums doing what they do in nature, but judging by the beetles’ family name, they knew what the insects were capable of: Derma is Latin for skin and este means “to consume.”

The first to use beetles in an institutional setting might have been Charles Dean Bunker, who joined the Kansas University Biodiversity Institute and Natural History Museum in 1895. According to the institution's website, Bunker was mostly concerned with the preparation of entire skeletons, and he “developed innovative techniques for cleaning bones, emphasizing methods for the maintenance of colonies of dermestid beetles.” Bunker’s students were called “Bunk’s Boys,” and they took what they learned from him and put it into practice when they went to other institutions.

That’s how Berkeley’s MVZ ended up with a colony in 1924. E. Raymond Hall, who had been one of Bunk’s Boys at KU, told Joseph Grinnell about the beetles, says Christina V. Fidler, archivist at MVZ, and Grinnell sent Bunker a letter requesting the bugs. Though there were issues with the methodology—“Bunker told him, ‘We had a problem with the beetles and our large mammals, and was infested by spiders,’” Fidler says—he sent Grinnell a colony anyway.

But MVZ’s colony didn’t revolutionize osteological prep at the museum as Grinnell might have hoped—at least not at first. The museum’s preparer, a woman named Edna Fischer, wasn’t interested in using the beetles. She thought they wouldn’t work, and instead boiled the bones, then cleaned specimens by hand, at a rate of 10 skulls a day. She was two years behind on skulls, and five years behind on skeletons.

Meanwhile, in the basement, 50 gunny sacks packed with specimens that had never been cleaned were full of dermestids doing what they do best.

The museum’s colony languished until 1929, when Fischer left and Ward C. Russell took over as preparer. He began using the beetles in earnest, refining the methodology as he went, and in 1933, he and Hall published a paper outlining their methods, “Dermestid Beetles as an Aid in Cleaning Bones,” in the Journal of Mammalogy—the first paper on the subject. Their aim was to speed up the prep time while creating better osteological samples, and they hit upon a solution: “By combining two common methods of preparation,” they wrote, “namely removing cooked flesh by means of instruments and exposing dried specimens to these beetles and their larvae, a system has been devised which we now feel justified in describing as possibly of help to others.”

Ward and Hall instructed scientists to find a warm room, and outfit it with wooden boxes topped with 3-inch strips of tin to keep the bugs inside. Next, they were to place a small, dried carcass in the box, drop some adult beetles on top, and leave them for a month. “At the end of this time,” Russell and Hall wrote, “the bugs have greatly increased in number and have consumed most of their meat supply. Conditions are then at an optimum for their use as cleaners of specimens.”

Now, finally, the real process of bone cleaning could begin. Hall and Russell advised scientists to line a shallow cardboard box with cotton; place a specimen to be cleaned inside, then cover it with more cotton, which would give the larvae a place to pupate. Those cardboard boxes were to be placed in the wooden boxes. Labeling the specimen was another matter: colleagues were instructed to use hardy paper (anything soft would be devoured or defaced by the bugs) with ink that could withstand both water and ammonia (which would be used to degrease the bones after cleaning) placed carefully inside.

Working with the beetles and using this method, Russell was able to clean a staggering 80,000 specimens during his 40 years at the museum. Even more impressively, the methods endure. These days, scientists at the Field and other institutions create colonies in much the same way Russell did.

But while the techniques stayed with the museum, some of the bugs didn’t: Russell took a colony home with him, Fidler says, and proudly showed it off to MVZ’s oral historians years after he retired.

A specimen dries in the beetle room at the Field Museum. Photo by Erin McCarthy.

 
Different natural history institutions house their beetles in different ways. At AMNH, for example, the beetles are kept in sealed metal boxes, and MVZ has two aquaria and one environmental chamber with multiple trays of beetles. Meanwhile, scientists at the Field mimic as much of the natural world as possible.

Former collections manager Dave Willard established guidelines that employees at the museum still use. Mesh tops give the beetles open air, and scientists turn the lights off at night to replicate the natural day/night cycle. To get the colonies to stay efficient, they’re kept at a constant temperature—around 70 degrees—and a constant humidity. And the amount of food in each tank must be just right.

It’s hard work, but it’s worth it—and Stanley thinks this extra attention to detail might be why the Field’s colony is especially vigorous. “I’ve never seen a better colony than the one here,” he says. “On any given day, when the colony is really cranking, we say that it’s hot—and we mean that literally. You can put your hand over the colony and feel the metabolic heat of the beetles. When the colony is like that, a mouse can take a little as an hour to clean.”

Preparing specimens for a trip to the beetle tank isn’t pretty—each has to be tagged, skinned, gutted, and dried, which both cuts down on the likelihood of rot and mold and makes the meat smellier, to better attract bugs—but learning about other methods of cleaning suddenly makes dermestid beetles seem like the best option by a mile.

Imagine boiling a skull until the flesh falls off, or burying a specimen too large for the beetles in elephant dung and compost, leaving it for a few weeks, and coming back to dig it up. Or steeling yourself to pull bones from a putrid barrel full of water, rotten flesh, and maggots. All are methods that natural history museums use, but each has their own pitfalls.

Once, when he was working at Humboldt, Stanley found himself facing five garbage cans. “Each of these garbage cans had a sea lion in it that had been macerating for months with maggots at the top,” he says. “My job was to fish through this goop and pull out the skeleton and clean off the rotting flesh. It was just disgusting.”

Macerating—in which specimens are dunked in water, allowing bacteria to feed for months so that flesh falls off the bone—totally works, Stanley says, but “the moisture and the activity by the bacteria are detrimental to the bones. If you aren’t incredibly careful, then femurs and humeri crack, and teeth will fall out of the skull.” Cleaning by burying can be disrupted, he says, and boiling is even more detrimental to the bones.

Stanley compares the beetle process to “putting a T-bone steak in the colony and coming back to find just the T of the bone.” Though a lot of people are grossed out by the beetles, it’s a relatively dry way to clean bones—and believe it or not, it even smells better than other methods. “If we were to show you some of the containers where we macerate things,” Stanley says, “it would be a lot worse.”

Dermestidae damage to a Manduca quinquemaculata specimen at the Texas A&M University Insect Collection. Image courtesy of Shawn Hanrahan, Wikimedia Commons //CC BY-SA 2.5-2.0-1.0.

 
If Dermestid beetles are the unsung heroes of natural history institutions, they also have the potential to be a museum’s greatest villain. “They are the method of choice for cleaning skeletons, but they are also one of the biggest threats for the very collection that we’re using them for,” Stanley says. “All of the specimens that are being prepared as study skins have dried tissue in them. If the beetles didn’t have anything else to eat, they would burrow into those skins and turn them to dust.

“If you get an infestation started in the collection,” he continues, “you are screwed.”

Take, for example, what happened at the South Australian Museum. In 2011, the museum’s insect collections—which included 2 million specimens collected over 150 years—were overrun by carpet beetles, and some holotype specimens (the first example of a species) were damaged. The Australian government allocated $2.7 million to eradicate the pests; museum staffers froze specimens for three months before moving them to special-built, nearly airtight cabinets.

“They can come in lots of different ways. You can bring them in on your clothes, your shoes, they can get in through ventilation or other access points,” Luke Chenoweth, an entomologist at the South Australian Museum, said. “They can decimate a specimen quite quickly, particularly the larvae. We had a large amount of dead insects in one place so it was the perfect environment for these pests to chew away.”

Museums don’t use carpet beetles, but what happened to the South Australian Museum could easily happen anywhere if a hide beetle were to escape, so institutions take special care to avoid this worse-case scenario. AMNH’s boxes have smooth sides and Vaseline in the corners so the bugs can’t climb out. Scientists also place sticky traps across the doors to contain any rogue beetles. (Another key is keeping them well-fed; when they’re hungry, they try to escape.) At the Field, the colony is on the same floor as its ornithology collection, right next to the bird prep lab, which causes scientists from other museums to “freak,” Stanley says. Elaborate mesh screens are used to keep flying beetles in place, and the double doors seal them off from other collections. At other institutions, the beetles are kept at more of a distance. MVZ has its colony in the same building, but on a different floor than the collections.

Institutions take other precautions, too. Just as a specimen must go through several steps before it gets into a beetle tank, it must go through several steps before it goes into collections. The process starts when scientists reach inside the tank, grab the specimen, and shake the beetles off. At that point, a skeleton might look clean, but, says Stanley, “Tiny larvae could be inside brain cavities or vertebral columns.” To make sure there are no stowaways, scientists freeze all specimens. (There doesn’t seem to be a set amount of time a specimen should be frozen; the Field freezes each specimen for 24 hours, while MVZ freezes for a week, places the specimens in quarantine for an additional week, and freezes again if necessary.)

Next, the bones are dunked in an ammonia solution—one part ammonia, nine parts water—to degrease them. The bones remain in the solution for 24 hours, then are picked at in the sink. “In theory, the beetles eat everything but the bones and the cartilage, but in practice, they often will leave little bits of tissue on the pads of feet for example or along the palette,” Stanley says. “So a lot of our volunteer time is spent with fine forceps and scalpels at the sink just to make sure that everything’s off.”

 
Only once a specimen has gone through all of these steps—freezing, dunking, and picking—can it finally move into the collections. Most will end up in boxes next in the museum’s miles and miles of storage, where researchers will pull them out for study—and potentially make important scientific discoveries. Others will end up on display in the museum itself, with most visitors none-the-wiser about how the skeleton was prepared.

“We’ve harnessed nature to study nature,” Stanley says. “If we could, we would use beetles every time.”