Dragonflies and damselflies - Order Odonata

Dragonflies and damselflies are large, conspicuous insects generally found near freshwater habitats. They are an ancient and successful group that was around long before the dinosaurs evolved.

One species of early dragonfly that lived around 250 million years ago was the largest insect known to exist and had a wingspan of over 70 cm!

Dragonflies success as a group is largely because of their fantastic flying abilities and their well-developed eyes. They are excellent hunters of other flying insects and can hover, move in zigzags, and even fly backwards. And they are fast - some of the larger dragonflies can reach flying speeds of 70 km per hour - possibly the fastest flying insects on Earth. Many people find their size and speed intimidating but, despite their powerful jaws, they are harmless. In fact, they do us a favour by eating many insects that bite us.

Dragonfly and damselfly facts

• There are over 6,000 species worldwide.
• There are 320 species known from Australia and about 100 of these occur around Sydney.
• The larvae are aquatic or semi-aquatic and are known as mud-eyes.
• Both adults and larvae are predatory.
• Adults are often found close to water, where they hunt flying insects.
• Adults' legs point forward, forming a basket to capture prey in mid-flight.
• Dragonflies are generally more powerful fliers than damselflies and most dragonflies have large eyes that almost meet at the top of their head.
• Damselflies often rest with their wings folded along their backs. Dragonflies usually rest with their wings held straight out from their body.

Dragonfly and damselfly Classification

Dragonflies and damselflies are large, conspicuous insects often found close to fresh water. The Order Odonata is divided into two suborders, the Anisoptera containing the dragonflies, and the Zygoptera containing the damselflies. Odonata closely resemble the oldest flying insects known from fossils. These fossil 'dragonflies' were very large, with one species reaching 71 cm in wingspan.

Dragonfly and damselfly Identification

Adult dragonflies are generally stout bodied and when at rest spread their wings out to the sides. Damselflies are generally more delicate and hold their wings along their body when at rest.

The larval stages of the two suborders can be distinguished by the placement of the gills. Dragonfly larvae suck water into their abdomen and move it over their internal gills. Damselfly larvae have gills at the end of the body as three appendages.

Dragonfly and damselfly Habitat and Biology

Like many insects, the larval and adult stages of dragonflies and damselflies differ in their shape and behaviour and use different habitats.

Eggs are laid into, or close to, water. The larvae adopt an aquatic lifestyle, with only a few exceptions. They feed on aquatic animals such as other insects, tadpoles and occasionally fish. Some larval dragonflies and damselflies are commonly known as 'mudeyes'. They are important in the diets of many aquatic predators such as fish.

Dragonfly and damselfly Lifecycle

After progressing through up to twelve larval stages the larvae crawl out of the water. Their skin splits and the adults emerge. The adults are predators that often capture prey while flying.

The adult stage has a pre-reproductive period that may last up to three weeks. At this stage the colour of the wings and body may change and the adults may disperse from their emergence point.

The reproductive phase may involve the establishment of territories by males, which are protected against other males of the same species. Copulation involves the male grasping the female behind the head with appendages on his abdomen while she bends her abdomen underneath his thorax to recover a packet of sperm that he has placed there. Adults may occasionally be seen flying in this tandem position.

Several species are endangered, such as the species that lives in peat bogs near Bowral and Robertson in the southern highlands and the hanging swamps of the Blue Mountains (both in New South Wales). This is because many Odonata larvae rely on precise water temperatures, good oxygen levels and unpolluted water to survive, and some of these habitats have been degraded. This sensitivity means that dragonflies and damselflies are important bioindicators of water quality.

Some species can tolerate poor water quality and low oxygen levels and at least one Australian species doesn't even develop under water, although it still needs a moist habitat.

References

• Watson, J.A.L., Theisinger, G. & Abbey, H.M. 1991. The Australian Dragonflies. CSIRO Publications, Melbourne.
• Watson, J.A.L. & O'Farrell, A.F. 1991. Odonata. In: Naumann et al. (eds.) Insects of Australia. Melbourne University Press, Australia.
• Corbet, P.S. 1963. A Biology of Dragonflies. Quadrangle Books, Chicago, Illinois.