Some can soar with the jets, 30,000 feet high, or fly at 40 mph. They mainly eat other insects, but one species can take down a small hummingbird.
But these fearsome predators also are graceful and ornamental fliers. Dragonflies and their slimmer cousins, damselflies, are all lovely creatures of the air. Their bodies are elaborately patterned. Their wings are splashed with color. Their iridescence shimmers as they swoop.
The duality of their image -- fierce but beautiful -- is also evident in the way they are named. There are dragonhunters and pondhawks, but also rubyspots and blue-fronted dancers.
They need sun for energy, but two dozen species turned up during a showery-day expedition led by the reigning local expert, Richard Orr. Orr has identified 109 species at the Patuxent National Wildlife Research Center, where the Aububon Naturalist Society-sponsored field trip was held.
These airborne jewels are most plentiful in summer, but around here they fly well into the fall. They need to be near water, be it pond, river or even temporary rain pool, to lay eggs. Unlike birds, they are active all day. And for every bird you see, says Orr, there are hundreds of dragonflies.
First, a short tutorial. If you are looking at an insect with a stout body that holds its wings out when resting, it probably is a dragonfly, male or female. If it has a slender body and holds its wings above its body when resting, it probably is a damselfly, male or female.
The area's most abundant dragonfly is the blue dasher, considered medium-size at about 11/2 inches long; it has a dusty blue tail with a black tip. One of the easiest to recognize is the common whitetail, which has a chalky-white body and black bands across its wings. It happens to like polluted ponds. Other species need a cleaner habitat, and Orr thinks that environmental deterioration is the reason he sees fewer along the Potomac River these days.
Big dragonflies are easy to spot, though sometimes it takes a good guidebook to figure out what you are looking at. But some are so tiny that they appear to be a twig on a blade of grass. About one species of damselfly, Orr says: "If it's so little you can't see it, it's a forktail."
They spend most of their lives in the water as larvae. They are in that state for an average of a year or two before shedding their skins and emerging with wings. For every adult, Orr says, 99 larvae hatch. They become snacks for raccoons, opossums and others. They caught a break this year, because predators were sated with the 17-year cicadas.
Perhaps it is fitting that such fetching fliers would devote 80 percent of their brains to vision, and they can see 360 degrees. They recognize another member of their species by looking at its face.
Dragonflies bend their three sets of legs into a basket shape to catch prey. Damselflies, which are not as strong, hover and catch their food by plucking it up. Their flying is unique among insects and gives them superb flight control, Orr says: They have two sets of wings, which they beat alternately. When the front set goes up, the back set goes down.
Although most dragonflies are local, some species migrate, arriving from the South in the spring, laying eggs and heading out in the fall. Orr has seen swarms of them that stretch for miles along the Texas coast.
Their ancestors go back many years. One, 250 million years ago, had a 27-foot wingspan.
Orr says it is a shame that some people are scared of dragonflies, although he concedes it is unnerving to see a big one zooming your way. But they are not interested in attacking people, he said. They are fairly innocuous. And they eat mosquitoes and deerflies -- what more do you want?"
-- D'Vera Cohn