Dragonflies
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 (i.e. Bees and Butterflies), or only flap the hind pair (i.e.
Beetles), or only have one pair (i.e. Flies), Dragonflies can flap or beat
their wings independently. This means the front wings can be going down
while the back ones are coming up. You can see this happening if you watch
closely. Dragonflies are excellent fliers, particularly the Anisopterans
and can loop-the-loop, hover and fly backwards quite easily. It is not unusual
for the larger species to reach 30kph and the Australian Austrophlebia
costalis has been clocked in at an impressive 58kph or 36 mph for short
bursts. They flap their wings relatively slowly though, at less than 30
beats per second. Compare this with 200 bps for a hoverfly or 300 bps for
a honey bee.
Information provided by: http://www.arthropod.net