dragonfly, any insect of the order Odonata, which also includes the damselfly. Members of this order are generally large predatory insects and characteristically have chewing mouthparts and four membranous, net-veined wings; they undergo complete metamorphosis. Species are found throughout the world except in the polar regions; the greatest variety occurs in the tropics.
Dragonflies, which are commonly called horse stingers and devil's darning needles, are strong fliers with elongated bodies; they rest with their wings outstretched. Some are 5 in. (12.7 cm) long. Damselflies are generally smaller, with slender, often brilliantly colored, bodies and rest with their wings folded back. The giant helicopter damselfly of tropical America has a wingspan of 7.5 in. (19 cm).
Both dragonflies and damselflies lay eggs on or near water. The nymphs are aquatic and breathe by means of gills located at the end of the abdomen; the gills can also be used for propulsion through the water. The nymphs feed on insect larvae and are an important food for fish and birds. When grown, they crawl up out of the water and molt. Most species produce a single generation each year, with the nymph stage usually overwintering. Both nymphs and adults prey on mosquitoes and other insects and are harmless, indeed beneficial, to humans.
Fossil remains of a form from the Permian period, with a wingspread of 21/2 ft (76 cm), have been found. Modern dragonflies and damselflies are classified in the phylum Arthropoda, class Insecta, order Odonata.
More on dragonfly from Infoplease:
See more Encyclopedia articles on: Zoology: Invertebrates