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Order Odonata
Dragonflies, Damselflies

General Description

The name Odonata is derived from the Greek "odonto-" meaning tooth which refers to the strong teeth found on the mandibles of most adults.

These animals are hemimetabolous (incomplete development {egg, nymph, adult}, immatures are aquatic (naiads), and they are also considered to be paleopterous (primitive wing structure, lacking the ability to fold the wings over the back).

Dragonflies and damselflies are a well known and fascinating order of insects.  They are divided up into two groups: (1) Anisoptera, the true dragonflies which rest with their wings out from their body in a cross shape and (2) Zygoptera, or damselflies who hold their wings above their body.

Dragonflies are a very ancient order of insects and fossils exist from more than 300 million years ago.  In addition, dragonflies are also relatively large insects, but in they past they were much larger.  Fossil remains of some dragonflies such as Meganeura monyi show a wingspan of 75 cm.

Morphological Characteristics

Immature:

Adults:

Biology

Dragonflies have strongly biting mouthparts and are active and aggressive carnivores, both as adults and as young, preying mostly on other insects. The adults have massive eyes which may contain as many as 30,000 individual lenses or ommatidia.  (Human eyes only have one lens each). Since dragonflies have such good eyesight, they have been known to respond to stimuli from more than 40 feet away. Their antennae are very small and poorly developed.

They have two pairs of almost equally sized long thin membranous wings; both pairs of wings usually have a stigma (a dark or coloured patch near the middle of the leading edge) and a mass of cross veins giving them the appearance of being a mesh.  Unlike most insects, which either flap both pairs of wings in unison or only flap the hind pair, or only have one pair, dragonflies can flap or beat their wings independently. They flap their wings relatively slowly, at less than 30 beats per second.

Dragonflies are unique among insects in that the males possess a set of secondary sexual organs on the 2nd abdominal segments as well as his primary sexual apparatus on the 9th segment at the end of his abdomen. Eggs are laid either endophytically (inside the living tissue of a plant) or exophytically (into or onto the water or the mud of the bank).   Nymphs are aquatic and breathe by means of gills .

After emerging from their eggs, dragonflies leave the vicinity of the water and go through a period of maturation, lasting about a month, a time where the gonads finish developing, and the body colour brightens.   This is also a time where many species disperse.  The adults usually feed on flying insects which they catch in flight or by sitting perched on a lookout post and sallying forth to catch passing insects.

Dragonflies are eaten as larvae by fish, water shrews, water beetles, water bugs, and birds.  Dragonfly nymphs also eat each other.  As adults they are also eaten by birds taking them as they are emerging from their larval skins and therefore helpless.

Distribution

Dragonflies and damselflies are common in freshwater habitats throughout the world.  In North America, there are 407 described species in 11 families;  Worldwide, there are over 5000 species in 29 families.

Economic Importance

Most dragonflies and damselflies are thought of as beneficial insects to some extent because they feed on small flying insects such as gnats and mosquitoes.  Conversely, they may also be regarded as pests to beekeepers when they eat honeybees.

Interesting Facts