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May 2010 cover image 12 Vulnerable Nursery

Wild Thing: Water Strider

For those floating and scooting water striders, it’s all in the legs.

By Sheryl Smith-Rodgers

Spend any time around a river or lake, and you’ll spot those long-legged, mosquitoey bugs called water striders that glide atop the water. As a kid, I always kept a wary eye out for them whenever I swam in the Blanco River. Though they never bothered me, I still worried that they might.

All these years later, I’ve learned that — unlike pesky mosquitoes — water striders avoid us humans. Instead, they go after small insects — living and not — that tumble into the water. Striders stay afloat via hair-covered legs that repel water. Their sensitive legs can also distinguish between the come-hither ripples sent by a prospective mate and the thrashing vibrations of a drowning insect. In the latter case, a strider grabs a victim with its short forelegs and then slurps up body fluids through its beak-like mouth (rostrum).

Photo by Dennis Kunkel

So how do water striders — aka Jesus bugs — walk on water? That question befuddled scientists for years. Many theorized that striders jetted around by generating their own waves. In 2003, however, mathematicians at the Massachusetts Institute of Technology solved the mystery. They even created Robostrider, a mechanical device made from lightweight wire, to show how the insects row with their middle legs and steer with their hind legs.

Math equations and hydrodynamics aside, I’m glad to know those mosquitoey bugs chow down on mosquito larvae as well!

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