Odonata
| Odonata | |
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| Dragonfly, Orthetrum cancellatum | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
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| Order: | Odonata Fabricius, 1793
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| Suborders | |
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Epiprocta (dragonflies), | |
Odonata is an order in the class Insecta, encompassing those insects commonly known as dragonflies (either when referring to the group as a whole, or for the species in the suborder Epiprocta in general or the infraorder Anisoptera in a strict sense) and damselflies (for the species in the suborder Zygoptera). The term Odonate has been coined to provide an English name for the group as a whole, in an attempt to resolve the problem caused by the dual meaning of the term dragonfly. This term is not however in common usage, and instead most Odonata enthusiasts solve the problem by using the term true dragonfly when referring to just the Anisoptera. This order has traditionally been grouped together with the mayflies and several extinct orders in a group called the "Paleoptera", but this grouping appears to be paraphyletic. What they do share with mayflies is the nature of how the wings are articulated and controlled (see insect flight for a detailed discussion).
It was long believed that the Anisoptera were a suborder and that there existed a third one, the Anisozygoptera (ancient dragonflies). However, they were combined in the suborder Epiprocta (in which Anisoptera is an infraorder) after it was revealed that the Anisozygoptera are a paraphyletic group composed of mostly extinct offshoots of dragonfly evolution.
These insects characteristically have large rounded heads covered mostly by well-developed, faceted eyes, legs that facilitate catching prey (other insects) in flight, two pairs of long, transparent wings that move independently, and elongated abdomens. In most families there is a structure on the leading edge near the tip of the wing called the pterostigma, which actually is a thickened, blood–filled and often colorful area called a cell. Cell in this case means a closed area of an insect wing bounded by veins. The functions of the pterostigma are not fully known, but it most probably has an aerodynamic effect and also a visual function. More mass at the end of the wing may also reduce the energy needed to move the wings up and down. The right combination of wing stiffness and wing mass could reduce the energy consumption of flying. A pterostigma is also found among other insects, like bees. Although generally fairly similar, dragonflies differ from damselflies in several, easily recognizable traits. Dragonflies are strong fliers with fairly robust bodies and at rest hold their wings either out to the side or out and downward (or even somewhat forward). Damselflies tend to be less robust, even rather weak appearing in flight, and when at rest most species hold their wings folded back over the abdomen (see photograph below, left). Dragonfly eyes occupy much of the animal's head, touching (or nearly touching) each other across the face. In damselflies, there is typically a gap between the eyes.
Odonates are aquatic or semi-aquatic as juveniles. Thus, adults are most often seen near bodies of water and are frequently described as aquatic insects. However, many species range far from water, seeking open fields and hilltops where they prey on smaller insects, catching these in flight. Dragonflies in particular are the raptors of the insect world and absolute masters of maneuverings in flight.
Eggs are laid in water or on vegetation near water or wet places, and hatch to produce nymphs that become (in most species) voracious predators on other aquatic organisms, including small fishes. The nymphs grow and transform into the adult flying insect. Male odonates have an organ near the back of the thorax in which they store spermatozoa; they mate by holding the female behind the head with claspers located at the tip of the male abdomen; the female bends her abdomen forward to touch the male organ and receive sperm.
Some very large species have been found in fossils. The largest odonates extant in the world today are the giant Central American damselfly, Megaloprepus coerulatus and Anax strenuus, a Hawaiian endemic dragonfly.
See also
External links
- Odonata of North America - diagnostic photographs and information
- Dragonflies and Damselflies (Odonata) of the United States - from U.S. Geological Survey (USGS). State-by-state listing of species with distribution maps, images and other information.
- Odonata of the World
- Worldwide Dragonfly Association
- Dragonflies and damselflies at the Odonata Information Network
- Asian-Dragonfly.net - you can ask questions and post information on Oriental Odonata
- Green Explorer - Checklists, photogallery, etc.. Dragonflies of Kerala, South India.
- Odonate Research at the University of Texas at Arlington