Saturday, July 18, 2009

Carrion Beetles – Nature’s Sanitary Engineers

One of the advantages of walking with one’s eyes cast to the ground is that one is likely to find all sorts of interesting things that exist at ground level: wildflowers, fungi, snakes, scats, tracks, bodies. Bodies? Sure – things are dying all the time in the woods, and if we are very lucky we might find them. The big question, however, is: “Why don’t we find them more often?”

Believe it or not, there is a lot of competition out there for dead things. You’ve got your vertebrate scavengers, like raccoons and coyotes, vultures and ravens, which sniff out and eat tasty morsels that haven’t been dead too long. Then you have your invertebrates that are looking for a good body to eat or to use for a nursery for the kids: assorted flies, ants and beetles. Underground there are soil-dwelling fungi and bacteria that would also like their share. No carcass goes unwanted, and thank goodness.

Last summer I came across a hairy-tailed mole right outside the Visitor Center. It was obviously dead, but as I watched, it seemed to reanimate! The body was moving! My curiosity piqued, I examined the body more closely and found not one, but two beautiful black and orange beetles working furiously at the body. They turned out to be a male and a female burying beetle (Nicrophorus carolinus), one of 46 species of carrion beetles found in North America. In the amount of time it took me to go inside for the camera, they had the body partially buried. Within half an hour it was gone.

Carrion beetles come in to general varieties: Silphinae and Nicrophorinae. The major differences between these subfamilies are behavior and morphology. The Nicrophorinae are the more interesting of the two (in my opinion) because they actively bury the carcasses they find.

First, the beetles must find the deceased, which they can do from up to a mile and a half away, detecting the fine chemical scent of decay (often within an hour of death) with their antennae, which can have some pretty nifty structures. Some have knobs, others fans or combs. These antennae are highly specialized to pick up long-distance scents. Once the body is found, the male and female beetles work together to bury it. Some may carry the body a short distance for burial, while others get right to work excavating beneath the corpse, which to the observer looks like it is slowly sinking into a miniature bed of quicksand. And just to show you how clever Mother Nature is, take note that the bodies of these beetles are flat, the perfect adaptation for scooting easily underneath a carcass, thus facilitating burial.

Why do these beetles bury the carcass, where as those in the subfamily Silphinae don’t? It comes down to a matter of taste. Nicrophorinae don’t like maggots. Flies are equally adept at homing in on death and for the same reason: they want to lay their eggs on the body, providing a nutritious food source for hatching larvae. Nicrophorinae will eat fly maggots, but they don’t like it when there are too many of them. In fact, they have been known to abandon a carcass if the maggot infestation gets too high. Silphinae, on the other hand, love to eat the maggots, so they are less picky and don’t bury the body. The more the merrier.

Once the body is safely secure underground, the female burying beetle lays her eggs on it and within a couple days the eggs hatch. Here is where another defining difference between the subfamilies comes into play: the adults will feed and defend their larvae. And before you know it, the larvae grow up, pupate and become adults, ready to find carcasses of their own.

As ubiquitous and common as carrion beetles are, they are not often found by the average person. This is partly because they (the beetles) are mostly nocturnal, but also because they do their jobs well and dead bodies are not around long enough for most people to encounter them. If you really want to increase your odds of finding some carrion beetles (and they are some of the largest and most colorful of our insects), you can investigate roadkills, or you can establish an abattoir on your property. I did this successfully, albeit unintentionally, the first year I began the losing battle with rose chafers. After collecting a quart of said pests (drowned in a mason jar), I left the jar out in the sun with the lid on for several days, forgotten. When I found it, I dumped the putrifying contents out on the ground. A few days later I came across the mess of rotting chafer bodies to find it alive with carrion beetles – beautiful yellow and black specimens as large as the end of my thumb. If only I could convince them to eat the live chafers…

So let’s all give three cheers for carrion beetles…and all the other creatures that work to keep our woods, waters, roads, deserts, etc. clean and healthy. If they weren’t out there consuming the bodies of the deceased, diseases would surely run rampant, or, at the very least, the world would be a smellier place. I, for one, am happy to share the planet with them.

Ellen Rathbone

Ellen Rathbone

Ellen Rathbone is by her own admission a "certified nature nut." She began contributing to the Adirondack Almanack while living in Newcomb, when she was an environmental educator for the Adirondack Park Agency's Visitor Interpretive Centers for nearly ten years.

Ellen graduated from SUNY ESF in 1988 with a BS in forestry and biology and has worked as a naturalist in New York, New Jersey, and Vermont.

In 2010 her work took her to Michigan, where she currently resides and serves as Education Director of the Dahlem Conservancy just outside Jackson, Michigan.

She also writes her own blog about her Michigan adventures.


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