Hairy Legs Help Bugs Walk on Water

Brian Handwerk
for National Geographic News
November 3, 2004

It's easy to understand why water striders—those six-legged insects that float and glide across the surface of ponds, streams, and lakes—are sometimes called Jesus bugs or pond skaters.

Less clear is how the bugs manage to stay afloat without drowning, especially in turbulent conditions brought by rainstorms or moving water. That is, until now.

Studying the insects under powerful microscopes, researchers in China have found that water strider legs incorporate thousands of microscopic hairs. Measuring about 50 micrometers—or less than two-thousandths of an inch—long, the hairs are scored by miniature groves. These groves trap air, increasing water resistance of the water's striders legs and overall buoyancy of the insect.

The team's research will be published tomorrow in the journal Nature.

"Normal hydrophobicity [or water repellency] may support them resting on water," said Lei Jiang, a researcher with the Chinese Academy of Sciences in Beijing, China, and study co-author.

"Slight touches or disturbances may break that balance. However, the air cushion at the leg-water interface can [enable] them to locomote quickly and stably on the water surface—even in rainstorms or other disturbances."

Jiang noted that other animals developed features, such as the feathers on a duck, that work in similar ways. However, most are far less effective at promoting super water-repellence, he said.

High Water Mark

Common to ponds, rivers, and lakes, water strides (Gerris remigis) are considered the most advanced surface-dwelling water bug found in nature.

The insects, which measure about a centimeter (two-fifths of a inch) long, have two pairs of long, thin legs that they use to float and travel on water surfaces. They also sport an additional pair of smaller frontal legs, which can be used to grab prey.

The water strider's hairy legs work to keep it afloat. The hair-and-trapped-air combination has such water-resistance qualities that the insects legs can create 4-millimeter (0.16-inch) dimples in a water surface without breaking through.

Continued on Next Page >>




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