Dragonfly

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A dragonfly is any insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera. It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body.

Dragonflies typically eat mosquitoes, midges and other small insects like flies, bees, and butterflies. They are usually found around lakes, ponds, streams, and wetlands because their larvae, known as "nymphs", are aquatic. Dragonflies do not normally bite or sting humans (though they will bite in order to escape, for example, if grasped by the tail); in fact, they are valued as a predator that helps control the populations of harmful insects, such as mosquitoes.

Life cycle

The life cycle of the dragonfly, from egg to death of adult, varies from six months to as much as six or seven years. Female dragonflies lay eggs in or near water, often in or on floating or emergent plants. Most of the life cycle is spent in the larval (nymph) form, beneath the water surface, using internal gills to breathe, and catching other invertebrates or even vertebrates such as tadpoles and fish. In the adult (flying) stage, larger species of dragonfly can live as long as four months.

General facts

Record breakers

Much larger dragonfly species existed in the distant past than occur on earth today. The largest one, found as a fossil, is an extinct Protodonata named Meganeura monyi from the Permian period with a wingspan of 70–75 cm (27.5–29.5 in). This compares to 19 cm (7.5 in) for the largest modern species of odonates, the Hawaiian endemic dragonfly, Anax strenuus. The smallest modern species recorded is the libellulid dragonfly, Nannophya pygmaea from east Asia with a wingspan of only 20 mm, or about 3/4 of an inch.

Dragonflies are the world's fastest insects, capable of reaching speeds of up to 97 km/h (60 mph). The Common Green Darner dragonfly (Anax junius) is nicknamed "Darning Needle" because of its body shape. It is one of the biggest and fastest-flying dragonflies, able to reach speeds of 85 km/h (53 mph). A study showed that dragonflies can travel as much as 137 km (85 mi) in one day. BBC. "Tiny tags trace dragonfly paths", 10 May 2006

Vision

Dragonflies have very good eyesight due to their unique eye structure. Dragonflies have up to 30,000 facets to their compound eyes; each one is a separate light-sensing organ or ommatidium, arranged to give nearly a 360° field of vision.

Camouflage

It was recently discovered that dragonflies employ a particular optical illusion, termed motion camouflage, to stalk other insects that invade their territory. A dragonfly can move in such a way as to project itself as a stationary object while speedily attacking its victims, new research suggests. These findings illustrate for the first time how dragonflies use complex camouflaging techniques during aerial combat.

Classification

Ancient dragonflies (Anisozygoptera)

Conventionally, the Anisoptera were given suborder rank beside the "ancient dragonflies" (Anisozygoptera, two living species and numerous fossil ones), but it has been determined recently that the Anisozygoptera form a paraphyletic assemblage of primitive relatives of the Anisoptera. Thus, the Anisoptera are reduced to an infraorder, forming the new suborder Epiprocta (dragonflies in a general sense). The artificial grouping Anisozygoptera is disbanded, its members being recognized as largely extinct offshoots at various stages of dragonfly evolution.

The oldest known dragonfly is the 320 million year old Delitzschala bitterfeldensis. Another old genus is Namurotypus.

Dragonflies vs. damselflies

Damselflies (Suborder Zygoptera) are often confused with dragonflies, but the two insects are distinct: most damselflies at rest hold their wings together above the body, whereas dragonflies at rest hold them out, either horizontally or slightly down and forward. Also, the eyes on a damselfly are separated, while those of the dragonfly are nearly touching. Both are members of the Odonata, and their life cycles are similar.

Some common species of the Northern Hemisphere

Emperor, Anax imperator
Keeled Skimmer, Orthetrum coerulescens
Black-tailed Skimmer, Orthetrum cancellatum
Common Whitetail, Libellula lydia
Migrant Hawker, Aeshna mixta
Azure Hawker Aeshna caerulea
Southern Hawker, Aeshna cyanea
Norfolk Hawker, Aeshna isosceles
Common Hawker, Aeshna juncea
Red-veined Darter, Sympetrum fonscolombii
Common Darter , Sympetrum striolatum
Vagrant Darter, Sympetrum vulgatum
Yellow-winged Darter, Sympetrum flaveolum
Broad-bodied Chaser , Libellula depressa
Four-spotted Chaser , Libellula quadrimaculata
Scarce Chaser, Libellula fulva
Green Darner, Anax junius
Downy Emerald, Cordulia aenea

References

External links

Odonata | Biological pest control agents

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