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"Whirligig" water beetles. Photo: <a href="">Zen Sutherland</a>, CC some rights reserved
"Whirligig" water beetles. Photo: Zen Sutherland, CC some rights reserved

Natural Selections: Whirligig Beetles

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Watching whirligig water beetles, found in circling clumps on the surface of calm fresh water, is a favorite childhood activity of many, including one-time child Martha Foley. Dr. Curt Stager explains the method behind their madcap collective behavior. (Note: Dr. William Romey teaches at SUNY Potsdam.)

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Why do Whirligig Beetles gather in large bunches? Are they mating? Keeping warm? According to studies done by Bill Romey of Clarkson University (at the time this was first broadcast) this occurrence is not a mating aggregation. The beetles stay together too long for it to be mating.

“He went so far as to mark some of them and watch them to see where they go,” says Dr. Curt Stager, “and he found a structure.” Romey found that females tend to be in the center of the group. In the cluster, there are around four different types of beetles. The females in the middle have usually eaten something. Outside this area, you will find males who have also eaten. Outside this, you will find whirligigs that have not eaten.

Whirligigs have a chemical defense system. They have two sets of glands, one in their abdomen and one in their thorax. Stager says, “They both emit this cocktail of chemical terpenes. Because of this, most fish do not like to eat them. I have seen trout that will come up to eat them and spit them back out.”

Some chemicals are also used for courtship and to help them glide through the water easier. The reason they clump is due to safety in numbers. The closer a whirligig is to a neighbor; the less likely it is to be eaten. It also protects the clump because even if one whirligig is killed or injured by a fish attack, this fish will spit it back out and leave the rest of the group alone.

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