Water Striders and Water Spiders

     Though they are from different orders of small creatures, common water striders and six-spotted fishing spiders have much in common.  And these handsome, interesting species demonstrate how the watery habitat they share shape them to be similar in appearance and habits to take advantage of that habitat to their advantage. 
     Both species walk on water surfaces without breaking through the surface film.  Both catch prey animals from the water's surface.  Both species are common in North America, east of the Rocky Mountains.  They live mostly on ponds and stretches of slow currents on streams.  And being cold-blooded, they are only active during warmer months.  But striders live on open water while the spiders dwell among shoreline vegetation and inch-deep water.  Their occupying different niches in the same habitat reduces competition for food between them.   
     Water striders are in the walking-stick family of insects.  Like all their family, they have six long legs that all emerge from the muscular thorax and resemble twigs for camouflage against predation.
     Water striders' bodies are five-eigths of an inch long, flattened, dark on top and white underneath for camouflage above and below these insects.  They look like the bottom from above and like the sky from a fishes' view from below.  Their front two legs are shorter than the rest and are used to grab helpless, invertebrate prey floating on the surface of the water.  The middle pair of legs are the longest and are used like oars to row the striders across the water's surface.  And the last pair of legs are like skates or skis that stabilize these insects on the water.  Some people call them water skaters.
     Adult water striders live several months and overwinter under fallen leaves on land near water.  They eat aquatic insects and land invertebrates that fall onto the water's surface and flounder helplessly, causing vibrations on the surface that alert the striders.  In summer, females spawn rows of cylindical eggs on objects at the water's edge.  The young mature in about five weeks on a diet of tiny invertebrates helpless on the water's surface.
     Six-spotted fishing spiders are greenish-brown with a white, lengthwise stripe along each side of the body.  They also have brown legs, 12 white spots on the upper abdomen and six dark spots on the lower thorax.  Male bodies are about a half-inch long while those of the females are three-quarters of an inch.  But with their leg span, each gender is about two and a half inches across.  
     Fishing spiders are alert to prey animals by putting some of their eight legs on the water's surface to feel for the vibrations of helpless invertebrates' floundering in the water.  Spiders that make prey-catching webs feel the vibrations of struggling victims in their webs through their legs.  The other legs of fish-catching spiders are anchored on lily pads or emergent vegetation near the shoreline.  These spiders are sometimes seen running across water plants on the water's surface.  And these spiders also catch tadpoles and tiny fish they see in the shallows along shore.  These spiders, in turn, are eaten by fish, frogs, small herons and other predatory creatures.
     Female fishing spiders lay their eggs into a white sac.  Each  stays close to her sac until the young hatch and disperse to be on their own.
     When by a pond or a sluggish stream in summer, watch for these intriguing invertebrates that have similar lifestyles because of the habitat they share.  The striders will be on open water, but the spiders will be among vegetation along the shoreline.