Thursday, August 6, 2009

When you're hot your hot

The Blue Dasher (Pachydiplax longipennis): this colorful little gem certainly deserves its name and it took no small amount of patience to sneak up this close to one. (The camera I'm using doesn't accommodate telephoto lenses).

A couple of shots showing the stripes on the thorax.

The next sequence of photos depicts the dragonfly engaging in a form of behaviour called "obelisking". According to most sources it appears this is a means for the insect to regulate its body temperature. Tilting the abdomen to a vertical position exposes it to less solar radiation, allowing the body to stay cool.

It wasn't a particularly warm day, about 20° C, overcast and windy, and the sun only came out for about five minutes, just long enough to provide illumination for these photos. According to this article, Obelisk posture (Wikipedia), obelisking can also be a threat display. Perhaps my close approach to taking these photos was invading the odonate's personal space ... this was his way of "giving me the finger" and telling me to buzz off.

This is a male Meadowhawk (Cherry-faced? Ruby? not sure which one) engaging in the same behavior. The day these photos were taken it was humid and the temperature was close to 30° C, plenty hot enough for the dragonfly to want to shed excess heat. But I think this is a threat display ... the closer I came with the camera, the higher the insect elevated its wings and abdomen. My prescence wasn't making him nervous enough to take flight, but he was getting "hot" under the collar (metaphorically speaking).

This male White-faced Meadowhawk (Sympetrum obtrusum) started obelisking but his nerves got the better of him and he took flight before assuming the fully vertical position.