This dragonfly doesn't perch like this for fun. His pose is a threat display.
This is a male Common Whitetail (Plathemis lydia), a showy dragonfly with a white pruinose abdomen and clear black-striped wings.
Common Whitetail males are highly territorial. They live near ponds, marshes and slow moving rivers where they defend 10 to 30 yards of the water's edge and conspicuously chase away all other males. When they're not chasing they pose like this to let the others know they mean business.
Their white pruinose backs are the warning sign. Pruinose refers to the dusty, frosted appearance caused by a pigment that covers the insect's "skin." In nature, pale-colored pruinescence often reflects ultraviolet light. If so, this bug probably glows in sunlight. I wish I could see it!
Female Common Whitetails look quite different because their tails aren't white, a feature that probably protects them from male aggression.
Watch near water and you'll see the males patrolling. Try to find the females too, even though they're not so flashy.
I'm happy when I see them. These dragonflies eat flying insects, including mosquitoes!
(photo by Chuck Tague)