Insect Spotlight: Beetle-whitened skeletons

Farm Forum

The skeletons seen meandering through darkened neighborhoods this time of year would be much scarier if they had juicy bits of flesh or hair hanging from their decomposed bodies. Indeed, this would be the normal state of skeletons if it weren’t for what should be Halloween’s favorite beetles, called dermestids.

Dermestid beetles, also known as carpet, hide, or larder beetles, are nature’s skeleton clean-up crews. Ask any skeleton or ghoul with a halfway decent memory, and he’ll tell you that larger animals and carrion feeders consume the tastiest morsels from a carcass soon after it dies, leaving small bits of cartilage, tendons, skin and hair on the bones. Rather than let the table scraps go to waste, dermestids converge on the remains of the carcass and get to work.

Traces of feeding by dermestid beetles on the skeleton can tell a bit about what happened to a corpse, be they killed by werewolfs, Frankenstein, or some random witch’s curse. Because dermestid beetles only colonize aged and exposed bodies, modern forensic science uses dermestid infestation on a corpse to estimate the time since death occurred, and where that death may have happened.

Archaeologists are also interested in dermestid infestations. Close personal friends to skeletons, the mummies of Egypt were frequently infested with dermestids. Sometimes the infestations were so intense that the dermestids made tunnels into the bones themselves, which served the beetles as pupal chambers.

Fairly recently, skeletons dating back to the Middle Bronze Age were found in Israel that had a sort of “honeycombing.” Initially this was thought to be the work some pathogen of the living person, or perhaps some human made damage to the bones by a chisel.

Using 3-D imagery to depict the tunnels into the bone and comparing it to modern dermestid burrows in wood and other materials, scientists were able to convincingly make the case that dermestids had infested the decaying bones before they could awake and torment trick-or-treaters. This fact gives us a glimpse into the funeral practices of these early cultures, which possibly did not entomb their dead as quickly as once thought.

Dermestids are so good at their jobs of cleaning up skeletons that a little industry has developed. Taxidermists and museum curators have long struggled with clearing the last bits of soft tissue from skeletons destined for display. Scraping or chemical clearing of the skeletons of animals can damage or leave stains on the bone.

There are a few small companies and museums that now keep large colonies of dermestid beetles, fed hamburger when not at work, in large, tightly sealed containers. When a carcass needs to be cleared, it is simply placed in the container with the beetle grubs, which quickly begin to work.

Depending on the size of the colony, skulls or skeletons can be meticulously cleaned by these little grubs in as little as a day or two.

With this in mind, no skeleton costume this Halloween is complete without a few beetles sewn onto or into the material. I strongly advocate withholding candy from any skeletons that are clearly imposters.

Jonathan Lundgren is a research entomologist in Brookings. Although interested in all aspects of insect biology, he specializes on insect conservation and reducing crop pests through the use of beneficial insects.