Odonata (Dragonflies)
Predacious insects with biting mouthparts and two equal or subequal pairs of elongate, membranous wings; each wing with a complex reticulation of small cross-veins and usually a conspicuous stigma. Eyes very large and prominent; antennae very short and fi
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ODONATA (DRAGONFLI ES) Predacious insects with biting mouthparts and two equal or subequal pairs of elongate, membranous wings; each wing with a complex reticulation of small cross-veins and usually a conspicuous stigma. Eyes very large and prominent; antennae very short and filiform . Abdomen elongate, often extremely slender; male accessory genital armature developed on 2nd and Jrd abdominal sterna. Nymphs aquatic, hemimetabolous; labium modified into a prehensile organ; respiration by means of rectal or caudal gills. Rather more than sooo species of these elegant insects have been described, included in over soo genera. They attain their greatest abundance in the Oriental and Neotropical regions and, except for Japan, no part of the Palaearctic zone contains an abundant or striking dragonfly fauna. Apart from the Hawaiian Megalagrion oahuense and a few others they are aquatic in their early stages. The adults, however, are not confined to the proximity of
FI G. 230
An Anisopteran dragonfly (Cordulegaster boltonii), male. Britain
O. W. Richards et al., Imms’ General Textbook of Entomology © O. W. Richards and R. G. Davies 1977
ODONATA (DRAGONFLIES)
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water, and the females of many groups seldom fly there except for pairing or oviposition. They are essentially sun-loving insects though some oriental species are only known to fly at night. Many are very swift on the wing and according to Tillyard Austrophlebia can fly at nearly 6o miles per hour; other species, particularly those of Coenagrion and Agrion, possess feeble powers of flight and may easily be caught. Although no existing member of the order can compare in size with the Upper Carboniferous Meganeura, which had a wing expanse of over 6oo mm, the females of Megaloprepus coerulatus measure about 190 mm across the wings.
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FIG. 231
B
A. Epiophlebia superstes, female. Japan B. Zygopteran dragonfly (Coenagrion puella), male. Britain Adapted from de Selys with wing-venation after Munz.
Adult dragonflies are generalized predators, usually feeding on almost any suitably sized insects (Hobby, 1934). They capture their prey in flight or while it is resting, using their forwardly directed legs to hold and transfer it to the mouthparts. Most species feed during the day but some species, when feeding on swarms of Culicidae, Chironomidae, or other Diptera, may do so at dusk or dawn (Corbet, 1962). In many species the mature males exhibit territorial behaviour, establishing themselves along stretches of water which they defend against other males and in which mating and oviposition take place (e.g. Moore, 1952; Jacobs, 1955; Kormondy, 1961; Johnson, 1962; Heymer, 1972). This behaviour tends to control the density of the species in the most suitable habitats, reduces disturbance to mating and egg-laying, and results in the dispersal of sexually mature males to new areas (Moore,
496
GENERAL TEXTBOOK OF ENTOMOLOGY
1953, 1964). Apart from local movements of this sort, some species such as Libel/uta quadrimaculata undertake longer migratory flights, sometim
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