Friday, September 01, 2006

Heart throb

Anyone who has watched a dragonfly scout a summer pond has seen one of the wonders of evolution.

A cross between a traffic-watch chopper and an F-16. A flawless match of form and function. A flying machine optimized for snapping up insects on the wing. And for sex. But more of that in a minute.

An old friend kindly sent me the new Stokes Guide to Dragonflies. What struck me first were the names: River Jewelwing, Smoky Rubyspot, Aurora Damsel, Vesper Bluet, Powered Dancer, Fragile Forktail, Sedge Sprite, Fawn Darner, Dragonhunter, Wandering Glider, Elfin Skimmer, to name just a few. If, as they say, Adam named all the creatures in Eden, he excelled himself with the dragonflies.

Every now and then evolution throws up a creature so perfectly adapted to its way of life that improvement seems impossible. Such species are rewarded by longevity. They survive for eons with little change, becoming what evolutionary biologists call "living fossils." The dragonfly is a living fossil, one of the oldest orders in the animal kingdom.

Sit by the summer pond and watch. One might as well be in a time warp. Glance up and see Triceratops grazing nearby. Or Tyrannosaurus rex. An asteroid smashes into the Earth and the reptilian giants become extinct; the dragonfly survives.

I have a special place for watching them, a plank bridge across a sluggish stream along my path. The males take up territories near the banks, perching on reeds or stones, chasing off intruding males, patrolling. It's a dominance sort of thing. The alpha male gets the chance to mate.

But there's a bit a business to take care of first. The male's genital opening is near the tip of his tail. The penis, however, is just behind the legs. So before he mates, he must transfer sperm from the tip of the tail to the penis up front.

Now he grasps the female behind her head with the tip of his tail. She curls her abdomen around and under until she brings her genital organ -- at the tip of her tail -- to his penis. Now their bodies are engaged in a heart-shaped valentine, one of nature's more engagingly semiotic acts of copulation.

(Click to enlarge.)