By itself, a male cicada pumps out a fair amount of noise for a bug. But a few thousand of them, packed wing-to-wing on tree branches, can sound at close range as loud as a subway train entering a station. Or a screaming child. Or a jackhammer.

So that is the volume: maximum. And the quality of the sound? Otherworldly. "Organic white noise," says David Kane, a Silver Spring composer.

Christine Simon, one of the country's premier cicada experts, a precisely spoken evolutionary biologist, resorts to Hollywood to find a metaphor. A mass of singing cicadas, she says, sounds like "flying saucers from a 1950s sci-fi film."

For the next few weeks, in the District and 15 eastern states, the insects' droning-hissing-clicking roar will become the outdoor soundtrack of this spring and early summer.

They quiet down come nightfall, if that is any consolation. And they do it, if not for love, at least for procreation. The males create all the din. The females, if they have been warmed by the sun and like what they hear, respond with a flick of the wings. In cicadaville, that means "Come hither."

Here is where we are so far in the tale of these once-in-every-17-years beasties. Early last week in the Washington area -- following the lead taken by cicadas in some warmer southern states -- the insects began crawling out of the earth. Emerging as nymphs, they molted into adulthood, shedding their tan-colored nymphal exoskeletons and unfurling crinkly, amber-veined wings to complement their black bodies and red eyes.

Many have died -- under foot, under wheel, between beak and jaw. Many have dodged their predators to crawl or fly into the treetops to bask in the sun some more.

Here and there, some males have begun to tune up. Gaye Williams, an entomologist with the Maryland Department of Agriculture, says she has heard individuals and small groups of cicadas in Annapolis. Cicada Web sites report similar rumblings.

Williams knows what the full blast sounds like, when the bugs gather in densely packed "chorusing centers." In 1987, she and a colleague were measuring the sound amid some cicada-infested trees in Fort Meade. She recorded readings in the mid-90-decibel range.

"It got to the point where your skin starts to crawl," she said. "It's the physiological effect of all that noise."

After they have mated, the females will deposit their eggs in the thin branches of trees. No later than early July, the noise will cease. All the adults will be dead. They will have spent 99 percent of their lives underground, and the tiny remainder up here with us, singing.

Cicada sounds have been celebrated by the Greeks of antiquity, Japanese haikuists and modern-day poets. Homer, in the Iliad, compares the discourse of "sage chiefs exempt from war" to the cicadas' song, according to J.G. Myers's 1929 classic study, "Insect Singers."

It seems that little or nothing in the way of a competing noise can disturb a group of chorusing cicadas. In the early 1900s, a French entomologist named Jean-Henri Fabre fired two cannon rounds near trees full of cicadas to see if they would stop. They didn't.

The males make their noise with sound organs known as tymbals, which include ribbed membranes that buckle back and forth the way a piece of metal does when popped in and out. Each species produces a distinctive sound. The dominant species emerging now, Magicicada septendecim, creates an "unvarying droning tone" when heard in mass numbers, says David Marshall, a University of Connecticut entomologist. Two other species will add hissing and clicking to the mix.

Only now are humans learning to make music as cicadas do. Tamara Smyth, a lecturer in musical acoustics at Stanford University, has borrowed from this structure to create what she calls the "tymbalimba," a device that allows a player to finger buckling ribs to control computer-generated sounds.

"I wasn't able to find one instrument that used that mechanism," she says.

David Dunn, a composer and bioacoustic researcher in Santa Fe, N.M., has spent a lot of time listening to insects and creating music from their sounds. He knows that most people's reaction to insect noises is "somewhere between a fear response and an annoyance response."

It does not surprise him that many people equate the sound of the cicadas with machinery: the humming of air-conditioners, the buzzing of power lines, the whirring of spaceships.

"Most of us live in environments dominated by those kinds of sounds," he says. "The sounds with which we have replaced the patterns of the natural world."

Part of his mission is to get people to listen to nature and its sounds. "It's really a matter of getting people back to paying attention, rather than reacting to them as if they were a disturbance."

For Marshall, who has studied periodical cicadas and their sounds, their music suggests what North America was like an eon ago, when these bugs rose to the top of an unpopulated continent's vast forests to chorus and cavort. "It gives me a sense of awe at . . . the scale of evolutionary time," he says.

In Silver Spring, composer Kane is getting ready to turn the tables on cicadas. He is writing a piece of music commissioned by the Strathmore Hall Arts Center in North Bethesda that is scheduled for performance July 29.

The working title is "Emergence: The Cicada Serenade." He has prepared for his work by listening to recordings of cicadas. "It's unlike any other sound I've ever heard in nature," he says.

But his ambition for his own piece is not to emphasize difference: "I want it to reflect the insectlike character of our lives . . . this vast rush to get things done before we vanish."