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(dragonflies and damselflies), an order of predatory insects capable of rapid flight. The large insects have a mobile head, large eyes, short bristle-like antennae, four transparent wings richly netted with veins, and a long, slender abdomen.
There are three suborders: Zygoptera, Anisoptera, and Aniso-zygoptera. The last suborder is common in Japan and India and includes a single genus, whose forms combine the features of the first two suborders. The Zygoptera have narrow fore and hind wings of nearly the same shape, which are pressed together and raised upward when at rest. In the Anisoptera the wings differ in shape and lie horizontally when at rest; the base of the hind wings is wide. The wing and the abdomen measure 10–94 and 14–120 mm long, respectively.
Dragonflies and damselflies feed on other insects that they seize in flight. They are considered beneficial owing to their destruction of mosquitoes, black flies, and other injurious insects. The insects do, however, spread protogonimosis, a dangerous disease of poultry.
Dragonflies copulate while in flight. The secondary copulative apparatus of the males is highly specialized and has no analogues among other insects. The eggs are laid in water, in the tissues of aquatic plants, or, less commonly, in wet soil. The larvae develop in water and breathe by means of gills. Zygoptera larvae have the trachéal gills at the caudal end, and the Anisoptera larvae have the rectal tracheal gills on the walls of the rectum, which is periodically filled with water. Metamorphosis is incomplete. The larvae have a very long lower lip that forms a prehensile organ, the mask, which protrudes when seizing prey and conceals the jaws when at rest. The larvae are predators, feeding on aquatic insect larvae and, sometimes, attacking tadpoles and fry. They serve, in turn, as food for fish.
At the end of the developmental period, the larvae emerge from the water and attach themselves to plants or uneven places in soil. The last molting occurs on land near a body of water. Some species can fly great distances away from water. During mass flights Libellula quadrimaculata forms a dense swarm stretching dozens of kilometers.
There are about 4,500 species, most of which inhabit the tropics and humid subtropics. About 165 species are widely distributed throughout the USSR except in arid regions.
REFERENCESZhizri zhivotnykh, vol. 3. Moscow, 1969. Pages 254–59.
B. R. STRIGANOVA