Logo

Dragonflies


by John Walsby


Of the many insects we associate with ponds and riversides, the most spectacular is the dragonfly. There are over a dozen species in New Zealand and the largest, the giant dragonfly, Uropetala carovei, is a handsome animal over 80mm long.

Dragonflies often have brightly coloured and patterned bodies but it is their spectacular aerobatic flight that first catches the eye. They are very ancient insects with fossil; examples being found in rocks more than 300 million years old. Some of those had huge wingspans over half a metre across.

Today's dragonflies have wings of a similar primitive design but they are masters of the air. They can fly very fast (some estimates claim more than 100km per hour) or hover motionless for long periods. They are also highly manoeuvrable, jinking and dodging sideways, putting on great turns of speed or sudden braking.

With the long straight abdomen behind, whirring wings and huge eyes on its large head, the dragonfly is unmistakable.Its excellent sight and masterly flight make it a formidable predator, taking other insects on the wing. All quiet waterways make good hunting grounds as many insects that have aquatic larvae visit to lay their eggs on the water weeds or the water surface.

Dragonflies also lay their eggs in water, often attached to weed. The nymphs are fully aquatic, breathing through gills. Like the adults they too are savage predators - but, instead of speed, they employ stealth and a flashing weapon.

Many live in underwater tunnels near the water's edge, hiding at the bottom during the day. At night they lie in wait at the entrance for insects, spiders, larvae or even tadpoles to pass close by. To trap these animals, the dragonfly nymph has a remarkable lower lip: a long double hinged plate with a pair of pincers on the end. It is called the mask and is snapped out forwards to grasp prey and draw it back into the mouth.


Back to Case History Menu

Back to Ecological Factors


Rivers Wetlands River Surveys

River Detectives Beaches Home