A male Blue Dasher (Pachydiplax longipennis)

Blue Dasher (Pachydiplax longipennis) obelisking

A male Blue Dasher (Pachydiplax longipennis)
A male Blue Dasher (Pachydiplax longipennis) obelisking on a hot summer day, Boulder, Colorado, USA. June 29, 2012.

Like all insects, dragonflies are ectothermic, which means their body temperature is regulated by their surroundings. This means that on cool days, they have to find ways to stay warm so they can fly, and on hot days, they have to find ways to cool themselves. A number of perch-hunting species can cool their bodies by a behavior called “obelisking,” where they raise their abdomens until the minimum amount of surface area is exposed to the sun. This way they can slow or even stop a rise in body temperature.

Oddly enough, despite having been seriously pursuing dragonfly photography for two years now, this is the first time I’ve been able to capture this behavior. Male Blue Dashers (Pachydiplax longipennis) sometimes raise their abdomens as a threat display to other males, but this one landed, raised its abdomen, and then carefully rotated around to point at the sun, so I’m fairly confident it was obelisking. Unfortunately, the photos where it was almost completely vertical weren’t quite as in focus as I would like, so you get the slightly less dramatic but more technically competent photo instead.

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