Water Striders

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Most of us have seen a water strider, gliding effortlessly on top of the water like an Olympic figure skater. These bugs have fascinated humans for centuries and also illuminate some interesting physical properties with their ability to walk on water.

These small insects belong to the family Gerridae and fall under the Hemiptera group of insects, otherwise known as “true bugs.” There are over 750 classified species of water strider, distributed over 67 genera. These bugs are found in literally every locale on earth, except for the Arctic and Antarctic. They even exist on remote islands in the Pacific and Indian Oceans.

Like all insects, water striders have a segmented body consisting of a head, thorax, and abdomen. They are generally small and measure about 2-12 mm, though some can get up to 25 mm long. They have a set of 4-segmented antennae and 6 legs; the front two which has pedipalp claws adapted for grasping prey.

Some species of water strider also have wings, while others do not. In general, wing length and size in water strider species depend on climate and how calm nearby sources of water are.

How Do They Walk on Water?

Credit: M. Gikas via Flickr CC-BY 2.0

By far, the most interesting behavior of water striders is how they walk on water. Water striders are able to walk on water as they distribute their body weight so as not to break the surface tension of the water. They have long legs that are flexible, so they can even distribute their body weight over a large area and their legs are coated in small, hydrophobic hairs that act as a kind of seal. Through the dexterous movement of their forelegs and hind legs, water striders can move across water surfaces at speeds up to 1 meter per second or faster.

These hydrophobic hairs also serve as a kind of buoyancy system. If the water strider is accidentally submerged in water, these hairs can trap air bubbles that lift the bug back up to the surface of the water. Notably, water striders have a lot of difficulties when there are substances in the water that affect its surface tension, such as oil.

Water Strider Diet and Life

Water striders are generally predators and feed on smaller organisms that are unlucky enough to fall into the water, mostly spiders and other insects. Stuffing prey in the water creates ripples, which guide the water strider to their food, similar to how struggling insects vibrate spider webs and broadcast their location.

Credit: J. St. John via WikiCommons CC-BY 2.0

Water striders can sense these ripples with their front legs and quick dart over to their source. They pierce their prey with a proboscis, inject it with saliva, and suck out the dissolved innards. Water striders prefer living prey but they will eat dead prey. They are also known to engage in cannibalism.

Water striders distinguish mates by the characteristic pattern of ripples they create. Through a pattern of signaling and responses using ripples, water striders find their mates, copulate, and produce offspring.