Thermoregulation
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"obelisking" Meadowhawk |
Thermoregulation is a technical word meaning "control of internal
body temperature". It is a major component of dragonfly behavior.
Dragonflies need to warm up their flight muscles
before being able to take flight. Heat can either be absorbed by
basking in the sun or it can be generated by shivering - a rapid
beating of the wings commonly referred to as "
wing whirring".
At other times, when the dragonfly needs to cool off, it
can be observed pointing its abdomen directly at the sun with its wings
rotated downward and tipped slightly forward to shade the thorax.
This is called
obelisking.
This position minimizes the surface area exposed to the
sun.
Some species lower their body temperature by making long
runs or patrols, diverting hot blood from their core area (thorax) into
the abdomen where it is cooled before being returned. Others simply perch
in the shade during the heat of the afternoon.
Varying color patterns can also aid in thermoregulation. In cool
weather darker colors move to the surface of the insect allowing more
heat absorption from the sun. In warmer weather light color patterns
help cool the insect. This change is the result of pigment
movements in the hypodermal cells of the exoskeleton. This is
especially common in dragonflies with blue or red markings such as in
the darner family. On a cool morning a blue Darner is more nearly dull gray
or pale lavender. As the insect warms up its original
blue color is restored.
A more detailed explanation is beyond the scope of this website. All you need to remember
is that both dragonflies and damselflies are genetically programmed to
regulate their body temperatures. Some
species, such as darners and meadowhawks, tend to be a bit
more developed than others and can be seen flying early
or late in the season in cooler temperatures.
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