Meet the water strider — an insect that walks on water

Look in any creek on a warm sunny day, and you're likely to see little spider-like creatures scooting on top of the water. These are water striders — not spiders — and they are remarkable little beasts.

First, look at those legs — wow! If a water strider pauses long enough, you can count six legs (if they were spiders, they'd have eight). The legs have inspired numerous common names for these bugs: Jesus bugs, water skeeters, water skippers, pond skaters. Their scientific family name is Gerridae. I'll stick with the name “water strider” for now.

Water striders make walking on the water seem effortless, if not miraculous. It does take effort on their part, and there aren't any miracles involved. There's a good scientific explanation. Water striders are equipped with six agile legs, two short, front legs and four long legs, behind. The two front legs are held as if in supplication (perhaps another reason for the name “Jesus bug”). These front legs balance the head just right and are always poised to snatch a meal. They have a rather cosmopolitan diet and will prey on just about anything.

Aft, there are long four legs that keep the bug's weight evenly distributed over the water. They also serve as oars. The tips of the legs have special water-repellent hairs. (The wonky term is hydrofuge.) The toes — well, tarsi — are set farther back on the legs so that they don't puncture the surface of the water. When the water strider rows with these oars, they push against the surface of the water, rather than breaking the surface of the water. They truly walk on water.

Some water striders have wings, and in fall they fly to the woods to hang out under logs and leaves. Evidently, this is a vulnerable time for them. Recently, I found a flotilla of water striders on a leaf in Ferson Creek in St. Charles, and every one of them had been chomped on by a predator.

Water striders overwinter as adults. They fly from the water to find shelter under leaves, sticks or rocks. In spring, it's back to the beach.

Spring is the time for courtship, and water strider males have quite the dance moves to attract females. The male strider hangs on to a twig or leaf in the water, and then sways the rest of his body in the water, making waves. The vibrations are picked up by females — and competing males — nearby.

In the language of water striders, ripple frequency says it all. A frequency of 3 Hz is an alluring courtship signal. Ten Hz is a warning, such as “Scram! She's mine!” Twenty-five Hz is the repelling signal, or “You're done for!” How do water striders read these messages? The legs have highly sensitive organs that pick up vibrations. These motion sensors work in split seconds (which is why it's so hard to catch one of these critters).

When males do their rock ‘n' roll during courtship, females make a decision (roughly speaking). If a girl picks up good vibrations from a guy, mating ensues. The female then lays eggs on floating objects in the stream. In about eight weeks, eggs will hatch into nymphs, and the life cycle continues.

There are many species of water striders in the world. The number depends on whom you ask. You can see a variety of the species around here if you poke around creeks and ponds. Some are larger than others, some are faster, and some, evidently, are tasty to other predators. As a whole, members of the Gerridae family of insects are semiaquatic predators. Of note on their list of food items is mosquito larvae. All the more reason to appreciate these bugs.

Water striders are fun to watch, and challenging to catch. Look for them on the surface of any creek during the warm weather. When the first frost comes, they'll be hunkering down — and we'll have to wait until next year to watch their miraculous moves on the water.

Valerie Blaine is the nature programs manager for the Forest Preserve District of Kane County. You can reach her at blainevalerie@kaneforest.com.