Dragonfly

For many, dragonfly is just an insect. 

For biologists, dragonfly is testimony to the power of evolutionary adaptation. A careful look at the fossil records confirms that dragonflies have been around for 300 million years, or a hundred times as long as humans. If dragonflies flew above the heads of dinosaurs during the Mesozoic Era and survived when the dinosaurs did not, this is by itself a great piece of evidence for their evolutionary success. The power of evolution, demanding though it is, has made dragonflies one of the oldest creatures on the planet.

With the announcement of the "extremely hot" weather from the effect of severe typhoon Bavi, I heard the forecast of temperature as high as 36 degrees Celsius over the weekend. I can't think of better outdoor activity than field trip of dragonfly watching. I ended up learning the way dragonflies make adaptation for thermoregulation. 

The first lesson from male crimson-tailed marsh hawk is the wax-like coating on their body, known as pruinescence. This beautiful dragonfly has a vibrant red abdomen, and a powdery (or pruinose) blue thorax. The wax-like pruinescence isn’t a pigment, but a “bloom” secreted by the insect’s cuticle to reflect harsh sunlight. So smart is it that it can cool down in hot weather. 

Another tactic is the blue dasher's posture at rest. The characteristic “obelisk” posture reminds me of my daughter’s handstand-like pose. Why does this dragonfly raise its abdomen into an almost perfectly vertical position, pointing the very tip directly toward the sun? Again, that has to do with thermoregulation for the cold-blooded insect. The vertical  body alignment significantly reduces the surface area exposed to direct solar radiation, thus avoiding overheating.

Cool.