Insect Picture of the Day

Click for larger version

Many a happy afternoon of my childhood was spent watching water striders. This one lazily skates in a back eddy of Pack Creek in Moab, Utah.

Water striders skate around atop of calm water utilizing surface tension to keep themselves afloat. They are clumsy on land and try to avoid fast-moving water, but on a calm surface they zip speedily along at nearly 1.5m/s–about 5.4km/h or 3.5mph. It was conjectured for years that they move by tweaking surface tension as well, but recent research has shown that it’s just good, old-fashioned rowing: The dimple shaped by each foot forms a long, edged depression in the water, and this is swept along the surface for propulsion.

If you look carefully at the larger version of the picture, you will see that this strider is camouflaged completely differently against aerial and aquatic predators. From above it is mottled brown to blend in with the creek bottom and hopefully to resemble nothing so much as a drifting twig or leaf. From below, however, it is a brilliant blue white to blend in with the sky. Water striders gravitate towards patches of dappled sunlight over shallow water. The shifting pattern of shade and sunlight makes it that much harder for fish to pick them out, and the shallow water makes it harder for bigger fish to get underneath them. This water strider is nearly 2cm long and would make far too large a meal for the minnows in this region of the creek.