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Back in the
Coal Age, nearly 300 million years ago, amphibians had already
appeared: Vertebrates that evolved from fishes, able to breathe and
crawl on land, but
returning to the water to breed. More remarkable, perhaps, were
another group also present in the Carboniferous Era, the
dragonflies. Remarkable because in their insect ancestry they had
become completely air-breathing, land-breeding animals, only to
return later to the water to develop an aquatic larval stage
complete with gills.
The submerged
larva or "nymph" of dragon and damselflies are highly predatory. It
lurks camouflaged among water plants and on the bottom mud, stalking
its prey like a cat. When prey is close, the front of the face opens
out into a scoop-shaped structure which is suddenly thrust out and
back, seizing the insect (or small fish) in an instant.
Jet-propulsion (expelling water from the abdominal gill chamber)
aids them in escape. If not eaten by a duck (or by another voracious
dragon "nymph"), the nymphs climb out (after doing a 1 - 3 year
stretch in the water) onto an emergent plant, split down the back,
pump up their new wings and dry in the sun. Then they spend a summer
- or probably two - expertly flying about to defend territory and
capture flying insects. While flying in tandem, a pair will mate and
sometimes continue flying together during egg-laying, making passes
close to the water. They rest at night on dewy grass. The big green
darners with clear wings may migrate south for the winter and live
perhaps another summer.
Damselflies
are more delicate, fly slowly, and hold their wings together over
the back when at rest. In contrast, the stout, fast dragonflies hold
the wings out at right angles to the body when perched, and the
degree to which the wings are lowered indicates how deep the rest
is. In most species the males are brighter than the female. A common
damsel has a bright blue body (female paler). The common marsh
dragonflies come in three main groups (not all to be seen here
unless siltation can be controlled):
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