Dragonfly, or Darning Needle, the name for an order of large, beneficial insects that feed on harmful insects such as gnats and mosquitoes. Dragonflies occur in the swamps and streams of all temperate and tropical regions. There are two suborders—damselflies and true dragonflies.
A dragonfly is an insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera. It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies are similar to damselflies, but the adults can be differentiated by the fact that the wings of most dragonflies are held away from, and perpendicular to, the body when at rest. Dragonflies possess six legs (like any other insect), but most of them cannot walk well. Dragonflies are some of the fastest insects in the world.
Dragonflies are valuable predators that eat mosquitoes, and other small insects like flies, bees, ants, and very rarely butterflies. They are usually found around lakes, ponds, streams and wetlands because their larvae, known as "nymphs", are aquatic.
Dragonflies generally are brightly colored with yellow, green, blue, or red spots or stripes that stand out against darker backgrounds. A dragonfly has a large head, bulging eyes, and strong jaws. Three pairs of medium-sized legs are attached to a short thorax, behind which is a long, slender abdomen. Two pairs of transparent, veined wings are attached to the thorax. Wingspan is from two inches (5 cm) to seven inches (18 cm). Dragonflies can fly forwards, backwards, and sideways, because at any one time their wings can rotate, move up and down, or move forward and backward.
Damselflies are smaller and more fragile than true dragonflies. Damselflies hover over reeds and grasses bordering ponds, where they obtain food by seizing other insects. At rest, damselflies hold their wings straight up from their bodies.
True dragonflies pursue insects through the air and use all six legs to seize the prey, which they then crush with their jaws. At rest, true dragonflies spread their wings flat, at right angles to their bodies.
Damselflies lay their eggs on soft plant tissue just beneath the water's surface. True dragonflies drop their eggs on the surface of the water. Both damselflies and true dragonflies pass through an immature aquatic stage that lasts several years.
Dragonflies belong to the order Odonata. Damselflies make up the suborder Zygoptera; true dragonflies, the suborder Anisoptera.
Courtesy : http://www.howstuffworks.com , http://en.wikipedia.org/wiki/Dragonfly
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