Water Strider

I was scheduled do part of a Nature Unleashed program last week at the Watershed Center with 4th grade students.  I found my station would be stream macroinvertebrates, one of my many weaknesses.  After a phone call Bob Ranney "volunteered"  to lead the sessions and bring me along.

As a group of us were talking before the bus arrived, someone asked what water striders ate.  Fortunately we looked them up on Google, for a few minutes later we were hearing high pitched voices asking "What is that spider on the water?"  Even a kid knows that what they are seeing is extraordinary, as a strider skims quickly across on top of the water.

Water striders mating- Wikimedia

Water striders are insects, predators of live and dead insects, worms, etc. that fall within their grasp, whether by floating up to the surface or landing on the water.  As true bugs they come equipped with a sharp rostrum in their mouth, "The better to suck up your body juices, my dear."  They can take on anything from a tiny mosquito larva to a butterfly or beetle.   They are said to be especially fond of worms which wash into the water after a rain.

Striders appear at first glance to have four legs because their other two front legs are short, modified to grasp their prey.  They "row" across the surface of the water rapidly with their middle legs, using the hind legs to both support their weight on the water and to steer.  Like other insects in the middle of the food chain, they are also prey for other species including fish, frogs and other amphibians.  Their only defense is their speed and agility. 

How do they manage to not only walk on water but to race at speeds equivalent to 600 mph?  The video at Richard Hammond's Invisible Worlds will explain this with beautiful low and high speed photography.

More detailed information on our common water striders is available at this Dallas Zoo site and more pictures are at fcps.edu.