Odonata (dragonflies 2, 3, 4, and damselflies)

Odonata fast facts

  • Large, with long bodies.
  • Large compound eyes with up to 30,000 ommatidia (facets), and three simple eyes (ocelli).
  • Minute antennae.
  • Specialised chewing mouthparts with strong teeth.
  • Legs end in a powerful pair of claws.
  • Two pairs of similar wings finely veined.
  • Fast, skillful fliers. Front and hind wings can move independently.
  • Wing beat is relatively slow at 20 - 40 beats per second.
  • Both adult and nymph are predators of many flies humans consider pests, e. g. mosquitoes, Tabanids, and blackflies. Nymphs aquatic and long lived.
  • Nymphs are preyed on by waterbeetles, water scorpions, notonectids, newts and fish, water shrews and small aquatic mammals.
  • Adults are preyed on by aquatic birds, insectivorous birds and larger dragonflies.
  • Females usually less colourful than males.
  • Dragonfly nymphs can be used to control mosquitoes. A few nymphs in a pond will eat 90% of the mosquito larvae.
  • Their presence is often used as an indicator of the health of streams and lakes.
  • 5,600 species worldwide, around 1200 south American species, 427 north American species, 130 European, 45 British Isles.
  • Hemimetabolous
  • Fossil record goes back over 320 million years in the Carboniferous when there were insects with wings like dragonflies.

Odonata, dragonflies, damselflies, are also sometimes known as horse stingers, devil's darning needle, which according to superstition will be used to sew up the lips of liars. They are divided into two sub-orders: Zygoptera, the damselflies, and Ansioptera, the true dragonflies.

Damsel flies usually have slimmer abdomens in both adults and nymphs. Both sub-orders usually fly during the day.

During the Permian there were huge dragonflies (with wingspans as large as that of a seagull today) to be found in what is now England. Meganeuropsis schusteri had a wingspan of 71cm. The atmospheric oxygen concentration was 35% (today it is 21%), which may have allowed more oxygen to reach further down the tracheoles (breathing tubes). Also the oxygen-rich atmosphere would have made flying easier. At that time insects were the only flying animals. It is believed that the huge dragonflies were slower fliers than those of today.

Odonata Wings and flight

The 2 pairs of wings of the damselflies are alike, whereas the hind wings of the dragonflies are broader than the front wings (see Libellula depressa).

At rest damselflies hold their wings vertically over their body, whereas true dragonflies rest with their wings spread out.

In flight the wings operate independently, unlike those of other strong fliers, e.g. wasps and bees who link both wings together. Wind tunnel studies, partly financed by the U S Navy and Air Force, have found that they twist their wings on the down stroke. This creates miniature whirlwinds that move the air much faster over the upper wing surface, and so reduces air pressure and increases lift. Over short distances they can reach speeds of 70 kph/45 mph. They can hover, and fly backwards and forwards.

The venation of the wings is used in identification to species level, however there is disagreement between entomologists in naming the veins, so identification for a beginner is usually easiest using illustrations.