Odonata (Dragonflies and Damselflies)

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Odonata

(Dragonflies and damselflies)

Class Insecta

Order Odonata

Number of families 28

Evolution and systematics

Odonates appeared by the early Permian period, and lineages corresponding to the three extant suborders flourished in the Mesozoic—Zygoptera and Anisozygoptera in the Triassic and Anisoptera in the Jurassic. Debate exists about the relationship of the three suborders; conventional classification fails to match the true evolutionary relationships of the groups, with "Anisozygoptera" being an artificial grouping. Zygoptera (damselflies) comprise four superfamilies and 18 families, the so-called Anisozygoptera has only one family and genus, and Anisoptera (dragonflies) contains three superfamilies and four families.

Physical characteristics

Wingspans range from 6.5 in (162 mm) in the Australian dragonfly, Petalura ingentissima, to 0.8 in (20 mm) in the Southeast Asian damselfly, Agriocnemis femina. They have large compound eyes and chewing mouthparts. The two posterior segments of the thorax are fused together. The legs are well developed for seizing prey and for perching; locomotion is almost solely by flight. The large, strong, multiveined wings usually have an opaque pterostigma near the wing tip. The tensegmented abdomen is long and slender. In males unique secondary genitalia evolved on the underside of the second and third abdominal segments, separated from the actual genital opening near the abdomen tip. Damselfly and several dragonfly females have well-developed ovipositors used to insert eggs into plant tissue; in some dragonflies the ovipositor valves are reduced, and eggs are dropped into water. Both sexes have caudal appendages at the tip of the abdomen, which in males work like claspers to grasp the female during mating. Larvae are aquatic and have a unique lower jaw specialized for grasping prey. Damselfly larvae are long and narrow and have three caudal lamellae used for breathing. Dragonfly larvae have broad bodies and breathe through tracheal gills located in the rectum.

Distribution

Dragonflies are found worldwide, except in frozen polar areas. Their greatest diversity is in the tropics.

Habitat

Larvae are mostly aquatic and are found under stones, buried in mud or detritus, or clinging to vegetation in stagnant and running freshwater. A few inhabit small water reservoirs in plants; others live in moist terrestrial burrows in forests. Adults occur over almost any kind of freshwater, where they mate and oviposit (lay eggs).

Behavior

Odonates regulate their body temperature by assuming different postures and selecting perching sites. In cool weather

they engage in wing whirring and land on sun-facing perches, whereas in hot weather they avoid overheating by assuming an "obelisk" position, with the abdomen exposing the least possible area to the sun. Many males are territorial and patrol an area of water, chasing rival males from it. Females cruise through territories, attracted to possible egg-laying sites. In some species, males perform threatening displays for other males or courtship displays for females by exposing color patches on the head, legs, abdomen, or wings. After emergence, some species undertake long-distance migrations; others disperse short distances when mature, searching for suitable sites to oviposit.

Feeding ecology and diet

Larvae and adults are active or ambush predators. Adults capture and eat insects on the wing, and larvae eat mosquito larvae, other aquatic invertebrates, and even fish and tadpoles. Adult adaptations for feeding include large eyes, which allow them to see in virtually all directions; legs forming a "basket" to scoop up prey; and strong wings, providing amazing flight maneuverability. Larvae capture prey by rapidly extending the labium and seizing prey between the two movable hooks at its tip.

Reproductive biology

Mating is unique. The male caudal appendages grasp a female at the back of the head (dragonflies) or anterior part of the thorax (damselflies), forming the "tandem position." Before copulation, the male arches his abdomen, transferring sperm from near the tip to the secondary genitalia at the base. Copulation ensues when the female arches her abdomen to bring her genital opening into contact with the accessory male genitalia, forming the "wheel position." After copulation, the female oviposits either alone or guarded by the male, who continues to hold her in the tandem position or flies near her. Eggs are laid in aquatic plant tissue, mud, or water. The growing larva sheds its skin several times before metamorphosing into an adult. Larvae live from six months to five years, depending on water temperature and food supply. The adult is the dispersal stage and lives from one to two months in temperate areas to a full year in the tropics.

Conservation status

Of the more than 5,500 known species of odonates, 137 are included on the IUCN Red List: two as Extinct; 13 as Critically Endangered; 55 as Endangered; 39 as Vulnerable; 17 as Lower Risk/Near Threatened; and 11 as Data Deficient.

Significance to humans

Despite menacing common names (e.g., "devil's darning needles" or "horse-stingers"), odonates are harmless; they have no sting. They consume large numbers of harmful insects (including disease-transmitting mosquitoes) and also are excellent indicators of freshwater quality. For the Navaho Indians they symbolize pure water. Traditionally known as the "invincible insect," the dragonfly was a favorite symbol of strength among Japanese warriors, and the old name for the island of Japan (Akitsushima) means "Island of the Dragonfly."

Species accounts

List of Species

Living fossil
Wandering glider
Forest giant

Living fossil

Epiophlebia laidlawi

family

Epiophlebidae

taxonomy

Epiophlebia laidlawi Tillyard, 1921, Himalayas.

other common names

None known.

physical characteristics

Black with bright yellow stripes on the thorax and abdomen. One of the only two extant species of Anisozygoptera, it shares some characteristics with damselflies (forewings and hind wings similar in shape and venation and a well-developed ovipositor) and others with dragonflies (eyes separated by less distance than their width, a pair of superior caudal appendages and a single inferior one in the male, and broad-bodied larva with rectal breathing).

distribution

Confined to the eastern Himalayas in Nepal and India.

habitat

Breeds in streams between 6,000 and 11,500 ft (1,800–3,500m). Adults fly in clearings within dense bamboo forests.

behavior

Larvae stridulate when disturbed. During the maturation period adults fly high above breeding areas. When mature, males fly slowly, low down and close to the stream; females skulk at the water's edge in the vegetation.

feeding ecology and diet

Nothing is known.

reproductive biology

Males grasp females by the back of the head to form the tandem position. A solitary female inserts eggs into the stems of plants growing at stream margins. Larval period lasts from six to nine years, the longest known for any odonate.

conservation status

Until 1980 considered Endangered but since then discovered at several new sites, appearing to be widespread and common. Given the necessary habitat protection, it can be considered safe.

significance to humans

None known.

Wandering glider

Pantala flavescens

family

Libellulidae

taxonomy

Libellula flavescens Fabricius, 1798, India.

other common names

English: Rainpool glider, globe skimmer.

physical characteristics

Yellowish-red in color. The base of the hind wing is noticeably broadened, with a small, diffuse yellowish patch at the base. Pterostigma of the forewing longer than that of the hind wing. Strongly tapering abdomen, with a black mid-dorsal stripe.

distribution

A cosmopolitan species, found in tropical and temperate regions around the world. Common in the tropics but rarely seen in Europe.

habitat

Breeds in small, shallow, often temporary pools. Adults frequently are observed far from water.

behavior

Strong, high-gliding flight, rarely settling. The species is gregarious and may form large feeding and migratory swarms. Feeding flights may continue beyond dusk. They have been seen far out at sea, flying even at night, when they frequently are attracted to the lights of ships.

feeding ecology and diet

A study of the gut contents of adults feeding over rice fields in Bangladesh showed that their diet consisted mainly of mosquitoes.

reproductive biology

Males patrol territories about 30–150 ft (9–45 m) in length. After mating, the male remains in tandem while the female lays her eggs. Females oviposit by tapping the surface of the water

with the tip of the abdomen. Larval development is rapid, an adaptation that allows for the use of temporary pools (including swimming pools) as breeding sites.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Forest giant

Megaloprepus caerulatus

family

Pseudostigmatidae

taxonomy

Libellula caerulata Drury, 1782, Bay of Honduras.

other common names

Spanish: Helicóptero.

physical characteristics

Largest damselfly, with a wingspan of 6.4 in (160 mm) and a very long abdomen, at 4 in (100 mm). Wings lack pterostigma and have a wide, dark blue band. Sexually dimorphic (males and females look different); males are larger, with a white patch before the blue band and a hyaline wing tip, while females are shorter, with only white on the wing tip.

distribution

Rainforests of Central and South America, from Mexico to Bolivia.

habitat

Larvae breed in water-filled plant containers. Adults frequent sunlit gaps or small clearings in the forest.

behavior

Because of their particular breeding sites scattered throughout the forest, this forest giant is never found in great numbers.

feeding ecology and diet

Adults are specialist foragers; they detect nonmoving prey and pluck small web-building spiders, occasionally also taking wrapped prey from webs. Larvae feed on mosquito and fly larvae, microcrustaceans and tadpoles, and conspecifics sharing the same tree hole.

reproductive biology

A territorial male uses a slow wing beat frequency to appear as a pulsating blue and white beacon to both potential mates and competing males in an open forest gap. He can aggressively defend a particular tree hole for up to three months. After copulating, the female uses her long abdomen to lay her eggs inside tree holes with water.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Corbet, P. S. Dragonflies: Behavior and Ecology of Odonata. New York: Cornell University Press, 1999.

Dunkle, S. W. Dragonflies Through Binoculars: A Field Guide to Dragonflies of North America. New York: Oxford University Press, 2000.

Needham, James C., Minter J. Westfall, and Michael L. May. Dragonflies of North America. Revised edition. Gainesville, FL: Scientific Publishers, 2000.

Silsby, J. Dragonflies of the World. Collingwood, Australia: CSIRO Publishing, 2001.

Westfall, Minter J. Jr., and Michael L. May. Damselflies of North America. Gainesville, FL: Scientific Publishers, 1996.

Organizations

British Dragonfly Society. Membership Office, 53 Rownhams Road, Maybush, Southampton, SO 16 5DX United Kingdom. Web site: <http://www.dragonflysoc.org.uk>

Dragonfly Society of the Americas. 2091 Partridge Lane, Binghamton, NY 13903 United States. Web site: <http://www.afn.org/iori/dsaintro.html>

Gesellschaft Deutschsprachiger Odonatologen. Web site: <http://www.libellula.org>

International Odonata Research Institute. E-mail: [email protected] Web site: <http://www.afn.org/iori>

Societas Internationalis Odonatologica. P.O. Box 256, Bilthoven, NL-3720 AG Netherlands.

Worldwide Dragonfly Association. P.O. Box 321, Leiden, 2300 AH Netherlands. Web site: <http://powell.colgate.edu/wda/dragonfly.htm>