Tuesday, June 19, 2012

Striders


My wife and I were sitting in the shade at Fallasburg Park Sunday afternoon. A clean stream gurgled at our feet, nearly to its Flat River destination. This portion of the creek was only 4-10" deep. A moderate current flowed in the middle of its 10-foot width, but slower and shallower along the inside turns.

Water Striders were active in the quieter water, so I attempted some photographs. Active? These guys were in perpetual motion it seemed. They were also very skittish. It required extreme patience to capture a few usable shots.

That opening photo holds a pattern you have most likely seen, but perhaps not examined. The black oval shadows on the bottom of the creek bed are caused by the Water Striders' feet "dimpling" the surface film of the water. The tiny depressions on top of the water scatter the light and create these distinctive shadows under the water.


(Click on any photo to enlarge)
Both of these insects are facing the upper left in this photo; upstream. Notice the different shapes of the shadows: rear legs point backwards (shaped like a sunflower seed); middle legs spread widest and with smallest shadows; front legs most rounded shadows. Note: the angle of the sun is also a factor in shadow shape.

More on the functions of legs later.


Description:

1/2 - 5/8 inches long. Flattened, elongate. Dark brown to black. Short forelegs. Middle and hind legs long and slender. Mostly wingless.

Habitat:

Surfaces of ponds, slow streams, and other quiet waters.

Food:

Aquatic insects, including mosquito larvae that rise to the surface, and terrestrial insects that drop into the water. They have piercing/sucking mouthparts which are very effective.

Life Cycle:

Courtship and mating involve communication by tapping ripples into the surface film.
Female lays parallel rows of cylindrical eggs on an object at the water's edge.
Nymphs mature in about 5 weeks. Young jump about actively. (Same for humans?)
Adults live many months.
In the northern parts of their range they overwinter under fallen leaves on land, near water.

Other:

These insects are called "skaters" in Canada. (Is this related to their passion for Hockey?)
In Texas they're called "Jesus Bugs" because they "walk" on water.




Here are two couples out for a Sunday stride.



These must be cousins, linked together for a raft trip, gently down the stream... merrily, merrily, merrily, merrily... (you know the rest).


Water Striders perform their floating feat by employing the surface tension of the water for support, plus their legs and feet are covered with numerous, microscopic hairs (less than 3 microns in diameter). They call them hydrophobic legs!




Here, you can actually see the little depressions under their feet; the "dimples" created in the water's surface.



Legwork:
  • The front legs are used as sensors to detect ripples caused by struggling insects on the water; potential victims.
  • The front legs can also puncture prey.
  • The long middle legs are used like oars for "rowing" and locomotion.
  • The longest hind legs allow a broad reach for better suspension on top of the water. Plus, they're used for steering while in motion.




Look carefully here, at the water's surface. See the many parallel streaks where the legs "dimple the water? It bends the light and magnifies the stream bottom. The "dimple shadows" are pretty cool too.



What would you call a large group of Striders? Swarm? Flock? Team? School?
Class dismissed!




While I was up the creek with my camera, a bunch of kids farther downstream were freaking out, and jumping out of the water, yelling "SPIDERS!" I wanted to teach them these fascinating facts that we just learned about the "STRIDERS". But it was Father's Day, they weren't my kids, and they weren't in my class.

But they could be...                                                                              ...just call "Father Nature".






Common Water Strider (Gerris remigis)

Resource:

The Audubon Society Field Guide to North American Insects and Spiders (Insects)


Photo Locations:

Fallasburg Park, (Fallasburg Park) Kent County, Michigan
Townsend Park, (Townsend Park) Kent County, Michigan