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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. |
