American burying beetle: We couldn't live without them
St. Louis Post-Dispatch
By Jeffrey Bonner
August 3, 2008
In the eighth of a monthly series this year, Saint Louis Zoo President Jeffrey Bonner explores a part of the globe where the Zoo is working to conserve threatened species, protect natural habitat and partner with other organizations to strengthen the web of life in which we all live. See story this story in St. Louis Post-Dispatch.
I think I'm getting a little too old to be a field scientist.
Recently I went out in Forest Park with some of our Zoo entomologists and I only lasted half an hour. They were looking for beetles and other insects by setting traps in Forest Park's beautifully reconstructed meadows. I get an allergy just looking at a picture of a meadow. Plus it was hot. And there were chiggers. (The good news is that chiggers can't process human skin, so if they bite you, they die. A little revenge goes a long way).
What pushed me over the top on the misery index, though, was our trapping technique. The bait is simple: a bucket full of five-day old raw chicken, buried up to its brim. Have you ever smelled a piece of raw chicken that has been sitting in the sun for the better part of a week? Try it some time. It will be a while before you visit the Colonel again.
The animals humans have the most contact with are invertebrates - animals without backbones. They're everywhere. We swat them and spray them. We vacuum them up by the thousands from our carpets, and we sleep with them in our beds every night. They bite us and burrow into us.
They also pollinate our plants. Without them, we wouldn't have much to eat. Equally important, they are Mother Nature's ultimate recyclers. Without insects and other invertebrates, dead things would simply pile up around us. We may not always like them, but we couldn't live without them.
Sniffing Out Death
In Forest Park, we were looking for one very important recycler: the American Burying Beetle, Nicrophorus americanus. It's about two inches long and has a shiny black armored shell, with bright orange markings on its back, wing coverings and head. It also has strong pincers, used for fighting and ripping through food. Its incredibly sensitive antennae can pick up a whiff of a mouse or quail carcass within an hour of its death and from as far away as two miles.
Strong fliers, the beetles converge on the dead animal, and the battle is on. There are rules that circumscribe the beetles' fight for the carrion: Males fight males, and females fight females. Usually the biggest, strongest male and female triumph, driving the other beetles away. The victors are now a couple, and begin the process of raising a family of their own.
Their first order of business is to find a suitable place to bury their dead trophy. They slide under the body, turn over on their backs and use their powerful legs to move the carcass, sometimes relocating it many yards away. Then they dig furiously, excavating the soil beneath the body and mounding it. Several hours later, the carcass is completely buried.
Working underground, the beetles strip away the fur or feathers of the dead mouse or bird. The adults must continually tend the carcass, removing any fungus that starts to grow and embalming it with an antibacterial secretion that slows decomposition, allowing plenty of time for the larvae to feed. They mate and the female lays her eggs in the soft soil around the preserved body, where they will hatch within a few days.
The larvae beg for food from their parents, who rip flesh from the embalmed corpse and regurgitate it. This goes on for about a week, until the young have eaten all but the bones. Then the adults fly away, and the young pupate in the soft soil, emerging about a month later as adults. Brood sizes average from 12 to 15. Interestingly, it appears that mom and dad make sure their offspring have enough food by eating excess larvae.
The burying beetle is not alone among insects that provide parental care to their young. Bees, wasps, ants and termites do much the same thing. The difference is that all of those insects are social insects living in huge colonies or hives. The burying beetle, amazingly, acts more like a human couple than a social insect (except for the part about eating their excess young).
The American burying beetle was once found in 35 states throughout the eastern and central United States, southern Ontario, Quebec and Nova Scotia. For reasons we're not sure of, they are now found only on Block Island off the coast of Rhode Island and in tiny patches in six other areas in the Midwest.
One theory is that they began to decline with the extinction of the passenger pigeon, a bird just the right size for a hungry mom and dad looking for a suitable host for breeding.
A more complex theory is tied to their place in the food chain. Years ago, large predators - wolves, bears and big cats - occupied the top position in the food chain. As hunting and the conversion of fields and forests to agriculture continued, these large predators were replaced by second-tier predators such as foxes, raccoons and skunks. They prey on smaller animals such as birds and mice, which the burying beetle prefers. Disease or light pollution at night (when burying beetles do their best work) also may play a role.
The American burying beetle has become one of the 12 major projects at the St. Louis Zoo's WildCare Institute. We breed them in five-gallon buckets, giving each pair a nice hunk of rotten quail on which to raise their young. Since we started late in 2005, we have reared 3,656 beetles. We track them genetically and recently released 128 pairs back to the wild in Ohio. By following them, we hope to learn why their populations declined so dramatically over the past 50 years.
Working with the U.S. Fish and Wildlife Service, we'd also like to reintroduce them in Missouri. But first we must make sure that there are no remnant wild populations left. To do this we've spent thousands of nights setting traps in 22 locations covering 14 counties. So far, we haven't found a single burying beetle.
Since the Pilgrims landed in 1620, more than 500 species, subspecies and varieties of our nation's plants and animals have become extinct. Why care about one species of beetle? They play a vital role as recyclers, turning rotten stuff into valuable nutrients. We know nothing about the antibiotic embalming fluid they produce, much less whether it could ever be of use to us. Finally, they are a wonderful indicator species: Understanding the reasons for their decline helps us understand what's happening to our environment.
The World Wildlife Fund puts it best: "All that lives beneath the Earth's fragile canopy is, in some elemental fashion, related. Is born, moves, feeds, reproduces, dies. Tiger and turtle dove; each tiny flower and homely frog; the running child, father to the man and, in ways as yet unknown, brother to the salamander. If mankind continues to allow whole species to perish, when does their peril also become our own?"
Republished with the permission of the St. Louis Post-Dispatch
Copyright 2008 St. Louis Post-Dispatch
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