Wednesday, March 23, 2016

A nemesis of museum collections

kw: natural history, natural science, insects, museums, research, photographs

Behold the dreaded Carpet Beetle. This species is the Varied Carpet Beetle, Anthrenus verbasci Linnaeus, 1767, the bane of natural history collections everywhere.

The adult beetle, seen at left, is typically less than 3mm long, and can be as small as 1.5mm (1/16 inch). The larvae are larger, to 4mm long. The two molts at right are typical of what we find when something organic, such as remnants of a dried snail or clam left in a shell, has been eaten. I've never seen living larvae, just their molted skins, and it is rare to find an adult beetle that has died in the shell box. Most frequently, a couple of molts and a lot of "frass", or dustlike beetle feces, are the only indication that a specimen's flesh has been consumed.

This is a species of "dermestids", members of the family Dermestidae, which also includes a group called Hide Beetles, because they are efficient consumers of leather and traces of meat. A natural history museums typically keeps a colony of Hide Beetles to use for de-fleshing skeletons. There is no better way to remove all soft tissues from the bones. I suppose that Carpet Beetles could work as well, but by using a larger beetle, they are better able to keep them contained in the "bug room"!

I recall one day a couple of years ago coming in to the research section on a Monday, to an awful smell. The curator of birds and mammals was there, cleaning up after a freezer that had broken down over the weekend. Most of the contents of the freezer had been small birds and smaller mammals such as mice, undergoing the usual treatment for pests before being skinned or otherwise prepared for storage. They were sufficiently freeze-dried that they didn't rot too badly over the weekend. A beaver carcass was another matter!

The beaver weighed 30 pounds, and the curator asked one of the volunteers for the day to help her prepare it. Wearing masks and gloves, they took it to the lab, returned to finish cleaning up the freezer room, then went to work: they skinned the beaver carefully, refreezing the skin until they could prepare it as a specimen; they removed and discarded the organs and cut most of the flesh from the skeleton and discarded it; then they carefully cut the skeleton into pieces "for the bugs". Only a portion at a time was put in the dermestid chamber, so as not to overwhelm the larvae. Portions not in the chamber were kept frozen. Eventually, they had a study skin, preserved and cotton-stuffed, and a beaver skeleton fully cleaned and washed and ready to be put in the collection.

Managed carefully, beetles and their larvae are quite useful. They're only a pest when they get somewhere you don't want them.

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