In the bug-eat-bug environment of the Adirondacks, a dragonfly turns out to be one of the best little friends a human being can have. Mainly, dragonflies eat flies and mosquitoes. Anything that keeps flies and mosquitoes from feeding on humans in the north woods qualifies as a force for good, and the adult dragonfly is supposed to eat something like 20 flies or mosquitoes an hour.

They are, in fact, nature's answer to the electric backyard zappers, which bring to the great outdoors all the ambience of a dentist's office.

This July, for reasons that the state's bug scientists have not yet quantified, there are a lot of dragonflies. Squadrons of them. More of them, it seems, than usual.

"That's a good sign," explained John Sheehan, communications director of the Adirondack Council. Mr. Sheehan, whose group warns against all kinds of environmental or other hazards affecting the park, explains that the dragonfly is an indicator species. More of them means a better ecosystem, generally.

The particular dragonfly that has been so plentiful in recent weeks is called the chalk-fronted corporal. The big iridescent ones, the ones whose images are converted into earrings and refrigerator magnets for souvenir shops all over America, are mostly the green darners. The green darners are the showboats, dragonflies à la Bob Mackie, and they arrive later. The corporals that appear earlier are the worker bugs, the rank and file of the dragonfly set.

Human swimmers in my section of the woods were particularly thankful this year for this sudden swarm of dragonflies, with their chalk-white bodies and shimmering steel-colored wings. To swim in an upstate lake means ducking one's head under the surface every few feet to get rid of the flies and gnats and mosquitoes, which can follow a human scent anywhere but underwater.

This year, as the flies circled a swimmer's head, the dragonflies flew into position and plucked off the little pests one by one. These airborne warriors could dive and twirl, their double wings giving them the kind of aerobatic agility that humans have yet to master, even with their mighty helicopters.

In midair, sometimes literally in front of a swimmer's eyes, a dragonfly would devour a hungry deerfly or an unwary mosquito. Suddenly, the buzzing was replaced by the whirring of a dragonfly's wings, the fighter escort from the insect world come to another human's rescue.

This guardian insect has a lot of human admirers, including the makers of at least one sci-fi horror movie. Milt Adams, a naturalist with the Adirondack Park Agency, explains that the dragonfly larva inspired makers of the movie "Alien." The larva, which can live for years before hatching into the air, has an extremely ugly mouth, which suddenly zips out and eats some unwary critter in three one-hundredths of a second. If it sounds disgustingly familiar, at least this tiny creature is on our side.