I came across an interesting dragonfly yesterday in a field and wondered what it was. After comparing the photo (above left) to a book I realized that it was an old acquaintance, a female common whitetail. I was irritated that I did not remember this critter since the male is so distinctive (see photo above right) that I can easily remember it. This led me to think about why a lowly insect would have a complicated system of sexual dimorphism whereby the male and female look nothing alike. The female also closely resembles the female of the 12 spotted skimmer although the males are not so similar.
Even the exalted birds that we love so much are sometimes not distinct in color or pattern between the sexes, or only slightly different. Why is this difference so apparent in an insect such as the whitetail? We generally think that insects are tiny automatons with limited behavioral scope.
Surely sex and territory are likely involved? Male whitetails are very conspicuous in their apparent patrolling of ponds and appear to be occupying a territory for the purpose of food gathering and providing egg laying sites for females. Their coloration is very showy and conspicuous, whereas the female is rather drab. This arrangement suggests that females choose the males they will mate with, perhaps both on their color and the quality of their territory. Female dragonflies of course do not sit on eggs like birds and do not need to be cryptic for that reason, but they clearly are subject to predation. Presumably the cost of greater visibility to the male is a greater risk of death from predation. Apparently It must be worth it or males would not be so conspicuously colored. Of course dragonflies are extremely swift and agile in their flight, but they are captured occasionally by birds.
So in our repeated attempts to learn some of the diverse array of dragonflies, it is perhaps some small comfort to know that they are more sophisticated creatures than you might imagine. They are certainly beautiful and interesting and definitely provide exercise for the brain! Watch for the amazing whitetail when you visit a freshwater pond.
Bill Dunson, Englewood, FL & Galax, VA