Whirligig beetles twirl and dance across the water

Look in a marshy pool or creekside eddy in spring and summer and you might see one of nature’s most spectacular swimmers – not a fish or amphibian, but a beetle that spins and twirls across the surface of the water.

“They have the most efficient swimming legs of any animal,” said Holly Roger of Wild Whatcom, who leads students on regular outings along the boardwalk at Tennant Lake Park near Ferndale, a common place to see whirligig beetles.

“It’s a super-good place to watch because they’re right there next to you” on the boardwalk, Roger said. “They can see under and above the water at the same time,” she said. “If you move your hand, they will dance back. It’s a defense mechanism against predators – birds and little kids with nets.”

Whirligig beetles are aquatic insects, members of Coleoptera, the same order as other beetles. They’re about  3/8 -inch long with a hard, flat and football-shaped back colored metallic black with yellow or orange legs. Their two front legs are longer, and their four shorter hind legs are fringed to help them swim.

Whirligig beetles carry an air bubble in their abdomen and breathe from it while under water. On the surface, they spin and swirl in frantic motion or trace lazy circles across the water. They dive when they feel threatened.

Another odd characteristic is their chemical defense system. They give off an odor that smells a little bit like apples, according to the website beneficialbugs.org.

This story was originally published March 15, 2017 at 7:00 AM with the headline "Whirligig beetles twirl and dance across the water."