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Water-boatmen


by John Walsby




There are a few species of insects that spend their whole lives in or on the water and rarely fly. While the adults are able to fly well they rarely use their wings except to escape to another pool should the one they are living in dry out.

Water-boatmen, back-swimmers, water measurers and pond skaters are all examples and are common insects of our ponds, lakes and quiet stream backwaters. They are all bugs related to more familiar examples, such as the cicada, aphid and the green vegetable bug.

Bugs are insects with piercing mouthparts inside a tube that looks like a hypodermic needle through which they suck up plant or animal juices. Bugs do not develop through larval and pupal stages as many other insects do but instead, nymphs - wingless miniatures of the adults - emerge from the eggs.

The water-boatman, Sigara arguta, is a plant feeder, sucking sap from water weeds below the surface. Supported and protected below water, these plants have soft stems that are easy to penetrate and feed from. Like any insect, the water boatman has three pairs of legs but from above only two pairs are visible. The forelegs are tucked away underneath and are only used to manipulate and steady the weed while the bug thrusts in its feeding proboscis.

The hind legs are very long and flattened and their surface areas are expanded by broad fringes of hairs along the edges. This equips them to function as a pair of strong oars to row the bug through the water.

The hooked middle pair of legs are used to grasp weeds under water when the water-boatman is not swimming, for a bag of air trapped around its abdomen by a coat of hairs makes it slightly buoyant. The water-boatman breathes from this air supply and when the oxygen in it becomes low, it floats to the surface to trap a fresh supply of air.

To find these insects, watch for their jerky swimming strokes. If you can catch one, you will see it is an attractive insect with a dappled meshwork pattern covering the back.


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