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.
