Buzz
Not long ago, the creature in the tank was a living bobcat, roaming and hunting as bobcats do, until its eventual demise. Now, it’s a skeletal mass resembling dried meat on bone, far from its former self. Surrounding it are swarms of tiny black beetles and bristly larvae, feasting relentlessly. If you listen closely, the tank emits a faint crackling sound, reminiscent of Rice Krispies in milk—a testament to the tireless activity of thousands of dermestid beetles.
The bobcat is being transformed into an osteological exhibit at Chicago’s Field Museum. Like many natural history museums globally, the Field employs Dermestes maculatus, or hide beetles, to prepare its specimens. The museum houses 10 colonies of these beetles, residing in aquariums within a secluded third-floor room. Inside the tanks, specimens are at different stages of preparation: one contains what looks like a sloth limb, while others display nearly clean skeletons still being scoured by beetles and larvae.
Nearby, on a countertop beside the sink, skinned and partially dried carcasses rest on racks and trays. “The beetles prefer slightly dried meat,” says research assistant Joshua Engel. He gestures to one specimen—“this is a seagull”—and then to another: “This one might be a beaver.” The room is filled with the pungent odor of decaying flesh. “You get used to it pretty quickly,” he adds.
If the idea of beetles consuming flesh from animal bones in a confined space makes you queasy, you’re not alone. However, despite the gross-out factor, natural history museums rely heavily on these insects, often calling them 'museum bugs.' Dermestid beetles offer several benefits over other bone-cleaning methods: they work quickly (a colony can strip a small rodent in hours or a large bird like a seagull in days), are less messy, and cause minimal damage to the bones. 'We love them,' says William Stanley, director of the Field Museum’s Gantz Family Collections Center, in an interview with mental_floss. He describes dermestid beetles as the unsung heroes of museums—as long as they stay contained.
D. maculatus larva. Photo by John Hallmén. Embed via Flickr.
The Dermestidae family includes numerous species, and if you look closely, you might find them almost anywhere. Have you noticed carpet beetles under your rugs or Khapra beetles in your pantry? If so, you’ve encountered a dermestid.
D. maculatus (also known as D. vulpinus) is found worldwide. Scientists at the American Museum of Natural History explain that these beetles undergo complete metamorphosis: egg, larva, pupa, and adult. The tiny eggs, about a millimeter in size, hatch within three days. The larval stage follows, during which the larvae molt seven or eight times, shedding their exoskeletons with each instar.
The larval stage is when the beetles are most effective. While both adults and larvae consume flesh, 'the larvae do the majority of the cleaning,' says Theresa Barclay, manager of the dermestid colonies at the Museum of Vertebrate Zoology (MVZ) at Berkeley. 'Adults eat far less.' The more larvae in a colony, the faster specimens are cleaned.
When the larva is ready to pupate, it does so within its own skin, bypassing the need for a cocoon. After five days, the adult beetle emerges, matures for another five days, and then begins its reproductive phase, mating and feeding for approximately two months. During this time, females can lay between 198 and 845 eggs. Eventually, they die, adding to the accumulating frass—a mix of crushed exoskeletons, beetle waste, and deceased insects—at the bottom of the tank.
While a single beetle lives for about six months, a museum colony can thrive for much longer, depending on the tank's size. Stanley notes that the Field Museum’s colonies typically last around five years, limited only by the buildup of frass, which eventually requires cleaning. 'It takes years for the dust to accumulate to the point where skeletons no longer fit in the tank,' Stanley explains. 'We stop feeding the colony, and it gradually dies off.' After freezing the tank for a week to ensure all beetles are dead, the contents are discarded, as frass isn’t suitable for composting. 'Then we have an empty tank,' Stanley says, 'and the process begins anew.'
However, this description makes the process seem simpler than it is. Perfecting the beetles’ role in museums has taken decades of effort, and initially, not everyone was convinced of their usefulness.
There’s no exact record of when naturalists first enlisted dermestid beetles for museum work, but their capabilities were evident from their name: Derma means skin in Latin, and este translates to 'to consume.'
Charles Dean Bunker, who joined the Kansas University Biodiversity Institute and Natural History Museum in 1895, may have been the first to use beetles in an institutional setting. According to the museum’s website, Bunker focused on preparing complete skeletons and 'developed innovative bone-cleaning techniques, including maintaining dermestid beetle colonies.' His students, known as 'Bunk’s Boys,' carried his methods to other institutions.
Berkeley’s MVZ acquired its beetle colony in 1924 thanks to E. Raymond Hall, a former student of Bunker’s at KU. Hall introduced Joseph Grinnell to the beetles, and Grinnell wrote to Bunker requesting a colony. Despite Bunker’s warning about issues like spider infestations in their large mammal preparations, he sent a colony to Grinnell anyway, as recounted by Christina V. Fidler, MVZ’s archivist.
However, the beetles didn’t immediately transform osteological preparation at MVZ as Grinnell had hoped. Edna Fischer, the museum’s preparer, was skeptical of their effectiveness. Instead, she boiled bones and cleaned specimens manually, processing 10 skulls daily. Despite her efforts, she was two years behind on skulls and five years behind on skeletons.
In the basement, 50 gunny sacks filled with uncleaned specimens were teeming with dermestids, naturally doing what they do best.
The museum’s beetle colony remained underutilized until 1929, when Fischer departed and Ward C. Russell took over. Russell embraced the beetles, refining their use over time. In 1933, he and Hall published a groundbreaking paper, “Dermestid Beetles as an Aid in Cleaning Bones,” in the Journal of Mammalogy. Their goal was to streamline preparation while improving specimen quality. They combined two methods: removing cooked flesh with tools and using beetles for dried specimens, creating a system they believed could benefit others.
Russell and Hall advised scientists to set up a warm room with wooden boxes lined with 3-inch tin strips to contain the beetles. They recommended placing a small, dried carcass in the box, adding adult beetles, and waiting a month. By then, the beetle population would have grown, and most of the meat would be consumed. 'Conditions are then at an optimum for their use as cleaners of specimens,' they wrote.
With the setup complete, the actual bone-cleaning process could commence. Hall and Russell recommended lining a shallow cardboard box with cotton, placing the specimen inside, and covering it with more cotton to provide a pupation site for the larvae. These boxes were then placed inside the wooden containers. Labeling the specimens required durable paper and ink resistant to water and ammonia, as softer materials would be eaten or damaged by the beetles, and ammonia would later be used to degrease the bones.
Using this beetle-based method, Russell cleaned an astonishing 80,000 specimens over his 40-year tenure at the museum. Remarkably, his techniques remain in use today, with scientists at the Field Museum and other institutions maintaining colonies in a similar fashion.
While the methods persisted at the museum, some beetles did not: Russell took a colony home with him, proudly displaying it to MVZ’s oral historians even after his retirement, as Fidler recounts.
A specimen dries in the beetle room at the Field Museum. Photo by Erin McCarthy.
Different natural history museums manage their beetle colonies in various ways. For instance, AMNH uses sealed metal boxes, while MVZ employs two aquariums and an environmental chamber with multiple beetle trays. At the Field Museum, scientists strive to replicate the beetles’ natural habitat as closely as possible.
Former collections manager Dave Willard developed protocols still followed by the museum today. Mesh lids provide ventilation, and lights are turned off at night to mimic natural daylight cycles. To maintain efficiency, colonies are kept at a steady temperature of around 70 degrees and consistent humidity levels. The amount of food in each tank must also be carefully regulated.
The effort is demanding but rewarding, and Stanley believes this meticulous care contributes to the Field Museum’s exceptionally robust colony. 'I’ve never seen a better colony than ours,' he says. 'When the colony is thriving, we describe it as ‘hot’—literally. You can feel the metabolic heat from the beetles by placing your hand above the tank. In peak condition, a mouse can be cleaned in as little as an hour.'
Preparing specimens for the beetle tank is far from glamorous—each must be tagged, skinned, gutted, and dried to prevent rot and mold while making the meat more aromatic to attract the beetles. However, compared to alternative cleaning methods, dermestid beetles emerge as the clear favorite.
Consider boiling a skull until the flesh disintegrates, burying a large specimen in elephant dung and compost for weeks, or retrieving bones from a barrel filled with foul water, decaying flesh, and maggots. These are all methods employed by natural history museums, each with its own drawbacks.
During his time at Humboldt, Stanley once encountered five garbage cans, each containing a decomposing sea lion. 'They had been macerating for months, with maggots swarming at the top,' he recalls. 'My task was to sift through the sludge, retrieve the skeletons, and remove the rotting flesh. It was utterly revolting.'
Macerating, a process where specimens are submerged in water for months to let bacteria decompose the flesh, is effective, Stanley notes, but it comes with risks. 'The moisture and bacterial activity can damage the bones,' he explains. 'Without extreme care, femurs and humeri can crack, and teeth may fall out of skulls.' Burying specimens can also be unreliable, and boiling is even more harmful to bone integrity.
Stanley likens the beetle-cleaning process to 'placing a T-bone steak in the colony and returning to find only the bone.' While many find the beetles unsettling, their method is relatively dry and, surprisingly, less odorous than alternatives. 'If you saw the containers we use for maceration,' Stanley says, 'you’d find them far more unpleasant.'
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.
While dermestid beetles are the unsung heroes of natural history museums, they also pose a significant threat. 'They’re the preferred method for cleaning skeletons, but they’re also one of the biggest dangers to the collections we use them for,' Stanley explains. 'Study skins contain dried tissue, and if the beetles run out of food, they’ll burrow into those skins and destroy them.'
‘If an infestation starts in the collection,’ he adds, ‘you’re in serious trouble.’
Consider the incident at the South Australian Museum. In 2011, carpet beetles overran the museum’s insect collections, damaging some holotype specimens—the first examples of their species. The Australian government provided $2.7 million to address the infestation. Staff froze specimens for three months before transferring them to specially designed, nearly airtight cabinets.
‘They can enter in various ways—on clothing, shoes, through ventilation, or other openings,’ explained Luke Chenoweth, an entomologist at the South Australian Museum. ‘They can destroy specimens rapidly, especially the larvae. With so many dead insects in one place, it was an ideal environment for these pests to thrive.’
While museums don’t use carpet beetles, the South Australian Museum’s situation highlights the risks of a hide beetle escape. To prevent this, institutions take stringent measures. AMNH uses smooth-sided boxes with Vaseline in the corners to stop beetles from climbing out, along with sticky traps near doors to catch any escapees. (Keeping the beetles well-fed is also crucial, as hunger drives them to flee.) At the Field Museum, the beetle colony is located near the ornithology collection, a setup that alarms visiting scientists. Mesh screens and double doors contain the beetles, while other institutions, like MVZ, keep their colonies on separate floors from collections.
Additional precautions are taken before specimens enter collections. After removal from the beetle tank, skeletons are shaken to dislodge beetles, but tiny larvae may still hide in cavities. To eliminate stowaways, specimens are frozen. Freezing times vary—24 hours at the Field Museum, while MVZ freezes for a week, quarantines for another week, and re-freezes if needed.
Next, bones are soaked in an ammonia solution (one part ammonia to nine parts water) for 24 hours to degrease them. Despite the beetles’ efficiency, they often leave small tissue remnants, such as on foot pads or palates. ‘Volunteers spend hours at the sink using fine forceps and scalpels to ensure every bit of tissue is removed,’ Stanley explains.
Only after undergoing freezing, soaking, and meticulous cleaning can a specimen finally join the museum’s collections. Most will be stored in boxes within the museum’s vast storage facilities, where researchers can access them for study and potentially groundbreaking discoveries. Others may be displayed in exhibits, with visitors unaware of the intricate process behind their preparation.
‘We’ve utilized nature to better understand nature,’ Stanley remarks. ‘If possible, we’d rely on beetles for every preparation.’
