Sunday, August 29, 2010

On thermoregulation in dragonflies

Brachymeria herbida - Tawny Pennant

As any mathematician will tell you, a group of objects with multiple attributes can be divided a number of ways. Dragonflies, for example, can be divided into species that spend a lot of time flying around ("fliers"), and species that sit around more and fly only short distances from their perches ("perchers").

Unidentified dragonfly

On hot sunny days, the dragonflies in the latter category, these so-called perchers, face the risk of over-heating. They reduce that risk by adjusting their posture, pointing their abdomen at the sun, thus minimizing exposure to the sun's rays. The top photos present two examples of perching dragonflies exhibiting this behavior.

Uracis imbuta (female)

Another strategy of course is to simply find a shady spot to perch.

I photographed these dragonflies yesterday in and around Suchitoto, El Salvador. If anyone can help me identify the second, smaller species, I'd love to hear from you!

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