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Sep 08, 2013 Features / Columnists, Interesting Creatures in Guyana
A dragonfly is an insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infra order Anisoptera known to have uneven wings because the hind wing is broader than the forewing. It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body.
Dragonflies can sometimes be mistaken for damselflies, which are morphologically similar; however, 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. However they are among the fastest flying insects in the world. In general, large dragonflies like the hawkers have a maximum speed of 10–15 metres per second (22–34 mph) with average cruising speed of about 4.5 metres per second (10 mph).
They are important predators that eat mosquitoes, and other small insects like flies, bees, ants, wasps, and very rarely butterflies. They are usually found around marshes, lakes, ponds, streams, and wetlands because their larvae, known as “nymphs”, are aquatic.
Some 5680 different species of dragonflies (Odonata) are known in the world today.
Though dragonflies are predators, they themselves are subject to predation by birds, lizards, frogs, spiders, fish, water bugs, and even other large dragonflies.
Formerly, the Anisoptera were given suborder rank beside the “ancient dragonflies” (Anisozygoptera), which were believed to contain the two living species of the genus Epiophlebia and numerous fossil ones. More recently it turned out that the “Anisozygopterans” form a paraphyletic assemblage of morphologically primitive relatives of the Anisoptera. Thus, the Anisoptera (true dragonflies) are reduced to an infra order in the new suborder Epiprocta (dragonflies in general).
The artificial grouping Anisozygoptera is disbanded, its members recognized as extinct offshoots at various stages of dragonfly evolution. The two living species formerly placed there—the Asian relict dragonflies—form the infra order Epiophlebioptera alongside Anisoptera.
Female dragonflies lay eggs in or near water, often on floating or emergent plants. When laying eggs, some species will submerge themselves completely in order to lay their eggs on a good surface. The eggs then hatch into naiads.
Most of a dragonfly’s life is spent in the naiad form, beneath the water’s surface, using extendable jaws to catch other invertebrates (often mosquito larvae) or even vertebrates such as tadpoles and fish. They breathe through gills in their rectum, and can rapidly propel themselves by suddenly expelling water through the anus.
Some naiads even hunt on land, an aptitude that could easily have been more common in ancient times when terrestrial predators were clumsier.
The larval stage of large dragonflies may last as long as five years. In smaller species, this stage may last between two months and three years. When the naiad is ready to metamorphose into an adult, it climbs up a reed or other emergent plant. Exposure to air causes the naiad to begin breathing.
The skin splits at a weak spot behind the head and the adult dragonfly crawls out of its larval skin, pumps up its wings, and flies off to feed on midges and flies. In flight the adult dragonfly can propel itself in six directions; upward, downward, forward, back, and side to side. The adult stage of larger species of dragonfly can last as long as five or six months.
Damselflies (suborder Zygoptera), typically smaller than dragonflies, are sometimes confused with newly moulted dragonflies. However, once a dragonfly moults, it is already fully grown. There are other distinctions that set them apart: most damselflies hold their wings at rest together above the torso or held slightly open above (such as in the family Lestidae), whereas most dragonflies at rest hold their wings perpendicular to their body, horizontally or occasionally slightly down and forward.
Also, the back wing of the dragonfly broadens near the base, caudal to the connecting point at the body, while the back wing of the damselfly is similar to the front wing. The eyes on a damselfly are apart; in most dragonflies the eyes touch. Notable exceptions are the Petaluridae (Petaltails) and the Gomphidae (Clubtails).
The largest living odonate by wingspan is a damselfly from South America, Megaloprepus caerulatus (Drury, 1782) while the second largest are females of the dragonfly Tetracanthagyna plagiata (Wilson, 2009). The female T. plagiata is probably the heaviest living odonate.
(Source: Wikipedia – The Free Online Encyclopedia)
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