Tuesday, June 02, 2009

Meet the Beetles

In Santa Fe the other week, I happened to meet a Ph.D. candidate who was working at the NIH, but who also got a gig writing copy for the Smithsonian’s Web site. She was in my group, and she was workshopping an article on the Smithsonian Institution’s Osteo Prep Lab about a hitherto unknown (to me anyway) “behind the scenes” activity at many natural history museums: cleaning the skeletons of large animals. That is, removing the flesh and connective tissue.

I was reminded of this topic today as I was investigating the topic of “what do they do with dead zoo animals?” (My initial response was, “Two words: snack bar,” but further digging happily disproved this.) One possible destination for zoo animals that have joined the choir invisible and are pushing up the daisies (etc. etc.) is being sent to places like the Osteo Prep Lab.

Which then brings me back to my original subject: how do they remove the flesh from large animals to study or display bones, skulls, or entire skeletons? Surprisingly, they do not use chemicals or “mechanical” means (which are best left to an overactive imagination). In fact, they use bugs.

Dermestid beetles are a family (Dermestidae) of about 500–700 species in the order Coleoptera. (This order comprises beetles, essentially, of which there are about 350,000 known species; indeed, beetles represent 40% of all known insect species and as much as one-fourth of all the species on earth! The great naturalist J.B. S. Haldane was once asked by a cleric what he might infer about the Creator and is supposed to have responded, “an inordinate fondness for beetles.” The quote is perhaps apocryphal, but no less true.)

Anyway, dermestid beetles are also variously known as skin beetles, larder beetle, hide or leather beetles, carpet beetles, and khapra beetles (but not “silver beatles” with an “a”). Some are called “bow beetles” as they make their homes in violin cases and feast on the hair used to make violin bows, which would make Isaac very stern indeed.

Given so many dermestid species, it’s not surprising that they have a wide range of habits, but most are scavengers, and various genera have carved out their own nutritional niche. Some eat plants, some animal hair, others feathers, and still others eat other insects such as wasps.

One particular genus—the Dermestes—are carrion eaters. That is, they eat dead animal flesh (well, so do we, but “carrion” specifically refers to dead and putrefying flesh; there are a couple of restaurants I could pick on here, but I shan’t). This gives them two useful purposes for us humans.

I have not seen CSI in many years, but I would be very surprised if they had never done at least one episode about Demestes maculatus—hide beetles—which are one of a variety of insects that play a role in the field of forensic entomology. That is, medical examiners can gauge the time of death by examining how much of a dead body has been munched by dermestids. Dermestids have been found to “dine out” about 5–11 days after death (a pretty wide range, forensically speaking, but scientists are working to refine that range; interestingly, different species seem to arrive on the scene first, probably senior bugs after the “early bird special”).

Getting back to my original point, dermestids are also used by many natural history museums to clean animal skeletons.

This is not new; the process actually dates from 1922, and the earliest published description of its techniques dates from 1933 (Raymond E. Hall and Ward C. Russell, “Dermestid Beetles as an Aid in Cleaning Bones,” Journal of Mammalogy, Vol. 14, no. 4, pp. 372–374, 1933). (Ward Russell is said to be the “father of dermestid beetle bone cleaning.” I’m guessing he took many meals alone.) A 1974 article from Curator sums up some of the refinements to the technique.

A page on the University of Michigan Museum of Zoology’s Web site written by Stephen Hinshaw sums up the current state of the art. Whilst some of it gets a tad judgmental (“do not remove the brain unless you are an incredible pansy” or “the fish people don’t care to have their specimens degreased. They say that is part of the fishy ambiance that they like in their work. On the other hand the bird division has an almost fetish desire to degrease their specimens”) it is a very good detailed look at the topic.

Essentially, these labs start a healthy dermestid beetle colony and when it’s up and running, add fresh specimens (i.e., full-fleshed bones) for cleaning. The bugs eat the flesh, lay their eggs in the decomposing flesh, and the young’uns get in on the feast. After a while, significant levels of “frass” build up and must be removed. (Frass is insect excrement. If you’ve ever seen the movie Sideways, you may recall that there was a big celebrity winery called Frass Canyon. The insult was intentional.)

Once the flesh is gone (this was the original opening line of the Mamas and the Papas’ hit “California Dreamin’”: “All the flesh is gone, and the bones are clean...”) , you wash the resulting bones, make sure there aren’t any little critters left on (or in) them, and they’re ready to be sent to other departments in the museum.

The caveats involved with working with dermestids are fairly obvious. First, you have to be careful not to let them escape or they will get into other parts of the museum and eat things you don’t want them to eat. (We all have relatives like this.) One solution involves keeping the temperature below about 80°, since Dermestes maculatus can’t fly at those lower temperatures, which helps matters greatly. Building a bug box (or “dermestarium”) that is sufficiently secure is one big challenge of creating a colony. The bugs also achieve their best results on larger specimens; creatures like fish or small mammals can be damaged during the eating process and “disarticulated.”

I also have it on good authority that some dermestid labs smell rather awful. It’s hard to see why; after all, they only involve large chunks of decaying flesh that are being eaten by bugs. It’s hard to see how that would have any unusual odors. At the same time, dermestid larvae have tiny hairs that can go airborne and cause problems for people with respiratory problems or allergies.

It probably goes without saying that there are other creatures used to clean skeletons, but dermestids are useful because they are thorough, easy to keep, and don’t damage the bone they are cleaning. And it’s more environmentally sound than using chemicals.

So anyway, the next time you are at a natural history museum looking at an elephant skeleton, just remember all the little people that went into its preparation. And then be sure to skip the snack bar.

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