Thursday, August 25, 2011
What if everyone could tell you'd had sex? Ask a dragonfly.Posted by Kirk Mona
So what about it?
Would you want everyone to know that you'd had sex? Some dragonflies like this male 12 spotted skimmer dragonfly don't seem to mind everyone knowing. I took the photo back on July 28th. When these dragonflies are young, their tails look much like the female's tails which are black and yellow.
As the males mature, the tails take on a pale blue wash. I had assumed this color change was a change to the actual color of the tail itself but this is not the case. Enter pruinosity. Pruinosity or Pruinescence derives its name from the chalky pale blue coloring on the outside of prunes. Some male dragonflies (notably the skimmers) develop a coating on their abdomen as they mature. It is a kind of waxy coating. The coating reflects ultraviolet light and may aid in attracting a mate.
What is interesting about the Pruinescence however is that it can be removed. If you look at the dragonfly in the photo at the top, you can see two darker marks, one on each side of the abdomen.These marks are where the pruinescence has been rubbed off by the legs of the female dragonfly during mating. If you look closely you can see smaller rubbed off spots from the other legs further up. By looking for these marks, you can tell if the dragonfly has mated or not. One would imagine the other dragonflies can tell as well.
I'm pretty glad we humans haven't evolved mating markers based on pruinescence. Human culture is complex enough as is.