Thursday, February 17, 2005

Insect Recyclers and Insect Fear Film Festival

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This Saturday the U of I’s Entomology Graduate Student Association will host the 22nd annual Insect Fear Film Festival, an event designed to get us thinking about bugs without dwelling on ways to kill them. The focus of this year’s festival will be forensic entomology, the science of using insect evidence in legal matters.

If you’re a fan of the television show CSI, or a reader of crime stories you know that often this means determining when a murder was committed by observing the development of the insect larvae found in the victim’s body.

Of course the insect larvae that most interest forensic entomologists are only a subset of the tiny critters that perform the ecologically essential work of recycling dead animals.

In the natural world, the death of an animal larger than a mouse triggers a fascinating and complex process.

The body is typically first discovered by adult blow flies—blue bottles, green bottles, or black—which, depending on factors such as weather and the accessibility of the corpse, may arrive on the scene within ten minutes of death, attracted by odors we cannot perceive. Blow flies quickly lay their eggs in wounds or the body’s natural openings. Within a day, these eggs will hatch and the larval flies—better known as maggots—will immediately begin to feed.

The next insect arrivals at a corpse are a second wave of flies, the flesh flies. To compensate for their somewhat later arrival, flesh flies deposit larvae that have already hatched within their own bodies, rather than eggs, on the corpse.

In his book, What Good Are Bugs?, retired U of I entomologist Gilbert Waldbauer notes that the presence or absence of flies makes an enormous difference in the length of time it takes for a corpse to decay. “Without them,” he writes, “a carcass decomposes very slowly and retains its form for months. If flies are present, 90 percent of the available soft tissue on the carcass is gone within 6 days.”

Maggots do not occupy a decomposing corpse alone for long, however. Other insects that feed directly on the body, such as carrion beetles, soon join them, as do predacious insects—various ants, wasps, and beetles—which come to make a meal of the maggots themselves. If you’ll pardon the expression, it’s a dog eat dog world down there!

As the soft tissue available on the corpse dwindles, two species of checkered beetles, which specialize in eating dried flesh, move in. These are also know as “ham beetles,” because they are just as happy dining on cured meats that humans produce—like bacon or ham—as food they find in the wild.

Finally, a few highly specialized forms of lice, beetles, and moths, move in to recycle even the materials that are indigestible for the rest of the animal world, feathers, claws, and hair.

Now, to some people it may seem gross to dwell too long on insects at all, let alone the insects that recycle dead animals. But if you want to get really really gross, you’ve got to think about where we would be without flies and their allies in decomposition.