Sanctuary. Volume 20 (2002), Number 4: 1–2.
A Miracle Among Miracles: The Life of the Water Strider
By John P. Roche
Figure: A Water Strider. (Photo by Bruce J. Marlin [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)].
Every day in the temperate months when the warm waters of streams, ponds, and puddles are filled with a churning soup of life, diminutive miracle workers play out their days in a complex but two-dimensional world. Water striders, members of the family Gerridae in the order Hemiptera, dance about on the surface of the water of bodies of water, clinging to the very force that holds water molecules together. They can suspend themselves and live their lives on the surface of water because their bodies are covered with small hairs that trap air, providing them with sufficient buoyancy to make the surface tension of water stronger than the force of gravity pulling down on their small bodies. As you have probably noticed, larger animals, like Labrador retrievers, tend to break through the surface tension of water rather quickly, their larger mass overwhelming water's relatively weak surface forces.
The water strider's ability to walk on water is indeed astounding--but this is not the only astounding thing about them. They manage to gather enough energy to live by rowing about, pushing off with their long middle pair of legs and maneuvering with their long back pair of legs, and finding mosquito larvae and other morsels floating on or just below the surface. Water striders are equipped with long piercing beaks. When they locate a suitable prey item such as a mosquito larva, they grab the item with their short, front pair of legs, pierce the item with their beaks, inject a digestive enzyme into the prey item, and then suck out the juices like a milk shake. That their choice of diet helps reduce the number of mosquitoes reaching adulthood is yet another of their laudable accomplishments.
Of course water striders need to do more than dance on liquid and eat mosquitoes to do well in nature's evolutionary play, and the water strider excels in this department, too. When seeking mates, a male strider stands on the water and taps out a rhythm across the water's surface. Females recognize this frequency and approach the male and mate, fertilizing eggs that will transform into the next generation of striders. Once females have mated, they lay their eggs on plants in the water. In seven to ten days, nymph water striders hatch from the eggs and swim toward the surface. Because they are so small, they have to expend considerable effort to break through the very molecular surface tension that will hold them up throughout their adult lives. Some do not succeed, and die in the process.
Once on the surface, some water striders live out their lives on the body of water on which their parents mated. Others, equipped with wings (some individuals of each species develop wings, some do not) fly away to new bodies of water, a capability that allows populations to flee the degradation of localized microhabitats and to capitalize on the opportunities offered by new ones.
That water striders can live successful lives on the narrow film between two media, water and air, is a miracle. But who is to say that there are not other miracles being made by other members of the insect world every hour of every day. Is the rapid, highly maneuverable flight of a dragon fly, the dance language of a honey bee, or the feeding acumen of a lady beetle any less miraculous? If we simply watch, every pond, every meadow, every wood lot holds many stories that can fill us with awe, with reverence, and with appreciation. If we wish to be reminded of this, of course, we can always take a hop off a dock into a cool pond, counting how many seconds we can remain atop the shimmering film at the pond's surface. And then, bobbing up, refreshed and humbled, we can look again at the water strider gracefully rowing past--and we can give thanks.
(Reprinted from Sanctuary, a publication of the White Memorial Conservation Foundation.)