dragonfly

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 abdomen); 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 (naiad, aka 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 ¾ of an inch.

Dragonflies are the world's fastest insects, capable of reaching speeds of up to 97 km/h (60 mph). ^[1] The Common Green Darner dragonfly (Anax junius) is nicknamed "Darning Needle" because of its body shape. It is one of the largest 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. ^[2]

Vision

Dragonflies have very good eyesight due to their 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^[3], 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 or held slightly open above (such as in the family Lestidae), whereas dragonflies at rest hold their wings horizontally or occasionally slightly down and forward. Also, the hindwing of the dragonfly broadens near the base, caudal to the connecting point at the body, while the hindwing of the damselfly is essentially similar to the forewing. The eyes on a damselfly are separated; in most dragonflies the eyes touch, with notable exceptions to this being in the Petaluridae (Petaltails) and the Gomphidae (Clubtails). 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

1. ^ Dragonflies. Retrieved on June 11, 2006.
2. ^ BBC. "Tiny tags trace dragonfly paths", 10 May 2006
3. ^ Dragonflies prove clever predators. Retrieved on June 18, 2006.

External links

• Dragonflies of North America - diagnostic photos and information
• Identification key to dragonflies found in Ireland
• British Dragonfly Society
• List of Anisoptera of the World
• Photos of most British species
• Dragonflies and Damselflies (Odonata) of the United States
• Green Explorer - Checklists, photogallery,... Dragonflies of Kerala, South India.