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Odonata = Photos-1, Photos-2

Introduction

Dragonflies and damsel flies are very abundant, but most are in tropical and subtropical areas. There more than 6,325 species known as of the year 2000. Most are brightly colored. All are predaceous both as nymphs and adults. The nymphs are almost all aquatic and feed on a wide variety of animals, including tadpoles, small fish and crustaceans. The adults capture their prey while in flight. The smaller species feed on mosquitoes and flies of similar size, while the larger species are able to capture the largest Diptera. Diptera, Hymenoptera and Lepidoptera constitute most of the prey. Mesothemis simplicicollis Say feeds extensively on adult Tabanidae in Louisiana, and Cacergates leucostica Burm. and others of that genus are effective predators of tsetse fly in Africa. They have been credited with marked reductions in tsetse population densities (Clausen 1940/62). The order is generally very beneficial, except in a few isolated cases such as in Russia where Aeshna cyanea Mull. destroyed about half the honeybee population in some areas. This occurred at the time of extended migrations and is attributed to a lack of the normal food supply. In America, Coryphaeschna ingens Ramb. may at times cause serious losses to beekeepers (Clausen 1940/62).

Lestes temporalis Selys is reported to be harmful to deciduous fruit trees in northern Japan because of its habit of making oviposition incisions in young shoots during July and August. Only trees located near water were injured, however.

Eggs are usually laid in incisions in stems of plants below the water surface, in muck or in rotting logs or they may be placed directly in the water while the females are in flight. There is simple metamorphosis, and the nymphs leave the water when mature.

Further Description

This order includes the dragonflies Anisoptera and Zygoptera. The name Odonata is derived from the Greek odontos (tooth) because there are conspicuous teeth on the mandibles. The size ranges considerably with Megaloprepus coerulatus of Central America and the Hawaiian Darner, Anax strenuus, being the largest. The extinct dragonflies belongubg to the Protodonata (Meganisoptera) were close ancestors.

This order also includes mayflies and several extinct orders in a group "Paleoptera." The way the wings are articulated and manipulated and general, but smaller appearance, indicates this relationship.

Odonata have large rounded heads with large compound eyes and two ocelli. Their legs are designed for catching, which is usually insects. There are 2 pairs of long, transparent wings that have independent movement. The abdomens are much elongated. The chewing mandibles are situated under the head in the adult.

Most families show a thickened structure called the pterostigma, which is located near the wing tip and which is thought to serve in aerodynamics and vision and may also aid in rapid wing movement.

The nymphs have thicker bodies and they are shorter than adults. They are apterous and have smaller heads thann the adult. The labium is modified to serve as a prehensile organ for catching prey. Damselfly nymphs absorb oxygen through external gills located on their abdomen, while dragonfly nymphs obtain oxygen through an organ located in the rectum.

To distinghish the two groups, dragonflies are strong fliers with tough bodies. They hold hold their wings either out to the side or out and downward when not flying. On the other hand, damselflies are not as strongly built, even, and when at rest most species hold their wings folded back over the abdomen. The eyes of dragonflies cover most of the head and almost touch each other at the top, while in damselflies there exists a larger gap between the eyes.

All species are aquatic or semi-aquatic as immatures and occur primarily around lakes and ponds and other bodies of water However, many species range far from water. They feed primarily on other insects.

Complex genitalia are found among males. There are grasping cerci for holding the female and a set of copulatory organs on the abdomen where the sperm are held after being produced by the primary genitalia. The male has its copulatory organ on the underside of the 2nd abdominal segment.

The eggs are deposited in water or on vegetation near water or other damp places. Pronymphs hatch and live from nutrients that were left in the egg. They then pass through 9 to 14 molts as nymphs feeding extensively on other aquatic organisms, including small fish. The nymphs change to pale flying teneral immature adults followed by reproductive adults.

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References: Please refer to <biology.ref.htm>, [Additional references may be found at: MELVYL Library]

Lohmann, H. 1996. Das phylogenetische System der Anisoptera (Odonata). Deutsche Entomologische Zeitschrift 106(9): 209-266.

Rehn, A. C. 2003. Phylogenetic analysis of higher-level relationships of Odonata. Systematic Entomology 28(2): 181-240.

Trueman, J. W. H. 2008. Tree of Life Web Project – Pterygote Higher Relationships.

Trueman, J. W. H. & R. Rowe. 2008. Tree of Life Web Project – Odonata. Dragonflies and damselflies.