Deep in the dirt from North Carolina to Connecticut, billions of cicadas have been waiting 17 years for a few weeks of sunshine, singing and sex in the treetops. Their time has finally come, and they began turning up Friday in Calvert and St. Mary's counties.
These revelers hatched back in 1979 and have spent the intervening years awaiting the right moment to make their appearance.
For squeamish humans, of course, there's never a "right" time for millions of big, noisy bugs to crawl out of the dirt.
The 17-year cicadas' dawn-to-dusk, 80-decibel mating calls can drive people nuts. Their sheer numbers, clumsy flight and surprise landings have freaked drivers and rattled wedding guests. And their carcasses can pile up in smelly heaps faster than eager cats and dogs can eat them.
But scientists are fascinated by the bugs' longevity and their mysterious 13- and 17-year life cycles -- both numbers with intriguing mathematical and evolutionary significance.
The good news for cicada-phobes is that this onslaught may not affect the Baltimore area. John D. Zyla, 32, a naturalist at Calvert County's Battle Creek Cypress Swamp nature center, thinks the 1996 batch is confined mostly to Southern Maryland.
Calvert and St. Mary's countians have told him the cicadas "were everywhere" in 1979. "They were very loud," he said. In the coming weeks, he hopes to pinpoint their range.
America's "periodical cicadas" first were reported by 17th-century New Englanders, who said the "flies made such a constant yelling noise as made all the woods ring of them, and ready to deaf the hearers."
They are called "periodical" because they emerge from the ground in vast numbers to mate only once every 13 or 17 years. But they don't all appear and disappear everywhere on the same schedule.
Different "broods," or populations of periodical cicadas, emerge in different years, in different places. This year's emergence in Southern Maryland is part of what entomologists call Brood 2, and they last emerged in 1979.
In May 1987, the Baltimore region was aswarm in cicadas when another population, part of Brood 10, crawled from the ground and began clamoring in the trees for sexual fulfillment. Their offspring are due back in 2004.
American entomologist Charles Marlatt first assigned the broods' numbers beginning with those that emerged in 1893. Some have since become extinct. Others are insignificant.
Brood 2 emerged in 1894, 1911, 1928, 1945, 1962 and 1979.
Tree-cutting, paving and development are reducing their range, but there are still 12 sizable broods of 17-year cicadas, and three broods of 13-year cicadas in the eastern United States.
Since Marlatt did his work, research and DNA analysis have shed light on some of the mysteries of the insect, often mistakenly called "locusts." Evolutionary biologists guess at others.
Why, for example, do cicadas live so long? And why do they emerge every 13 or 17 years? Is it an accident that each life span is a "prime" number, evenly divisible only by one and itself?
The cicadas' six species all belong to the genus Magicicada. They are distant cousins to the more familiar two- and three-year cicadas, some of which emerge each July or August.
Magicicada spend all but a few weeks of their lives underground, sucking on tree roots. After somehow noting the passage of 13 or 17 years, they dig neat, round, escape shafts to the surface. When the soil warms to 64 degrees or so, they all emerge in a
Finding a vertical perch, the nymphs split their dry skins, and pale, winged adults climb out to begin an urgent search for mates.
Each brood contains several species, and they have just a week or two to sort each other out. The males call by vibrating two round organs called tymbals under each wing. Multiplied by millions, the songs become a lusty din that attracts members of like species to treetop "chorus centers."
After they mate, the females disperse, and each one slips up to 600 eggs into cuts in the tips of tree branches. In six to eight weeks, the eggs hatch, the nymphs drop to the ground and burrow into the soil to feed for another 13 or 17 years. Their parents die.
The cicadas' egg-laying wilts nearby leaves and can damage orchards. But otherwise they're harmless, and homeowners are urged not to run for the bug spray.
No one knows why cicadas evolved their unique life cycles. But scientists have lots of ideas.
"It's all speculation," said Dr. Chris Simon, an associate professor of evolutionary biology at the University of Connecticut and author of a summary of scientific thinking on the periodical cicadas.
"My idea is they lengthened their life cycle to become synchronized," she said. The nymphs develop at widely varying rates. Because there is safety in numbers, the faster ones evolved an ability to delay their emergence until the others "catch up."
"To do that, you have to extend your life cycle," she said.