Every 17 years they emerge. To some, it's a dream come true: an opportunity to see nature in full-blown action. To others it's a waking nightmare: the invasion of the really big bugs with the big red eyes.
The periodical cicadas of Brood X (that's a Roman numeral 10) are coming. If you live on the East Coast from New Jersey to Georgia, or in parts of the Midwest (see map) watch for them. At press time, they had begun to appear in Indiana, Tennessee, Kentucky, Virginia, Washington, D.C., and Maryland.
Why "Brood X"? Think of a brood as a "graduating class" of periodic cicadas (sometimes mistakenly called "17-year locusts"). Different groups of periodic cicadas appear at different times, depending on when they hatched. Scientists have kept track of these different "batches" or broods. They have given Roman-numeral names to 15 of them. Twelve are 17-year broods, and three are 13-year broods.
Some years, two or more broods will overlap and appear in the same year. Other years, no periodic cicadas will emerge. This year, Brood X emerges, the biggest batch of them all.
Brood X "graduates" are expected in parts of 15 states. The heaviest concentrations will be in sections of Indiana and Ohio. They can expect anywhere from 100,000 to 1.5 million cicadas per acre in places. Brood X is the largest insect emergence in the world. It will involve billions and billions of insects.
Don't worry, though. While the insects may be inconvenient (loud, for one thing, and crunchy underfoot for another), they do not bite or sting. If one of the insects lands on you, it's just because it thinks you're a tree. In fact, for many animals - and some humans - Brood X will be a banquet! (Stir-fried, newly emerged adult cicadas taste like canned asparagus.)
Jean Pearson remembers a cicada emergence in the late 1930s in Washington, D.C. Says Ms. Pearson, "The sidewalks were carpeted - sometimes ankle deep - with the bodies of cicadas, and between the humming and the sound of them crunching underfoot, it's like the whole city was alive." Again, there's no telling where the highest concentrations of cicadas will be. (And one assumes that Washington's street-sweepers are more efficient these days.)
But think of the outdoor graduations, weddings, and family picnics that are scheduled for early summer. Those folks may want to rethink their plans.
Brood X cicadas are actually three different species - Magicicada septendecim, Magicicada cassini, and Magicicada septendecula. Many of us have annual or "dog day" cicadas where we live. (They are called "dog day" because they usually emerge in late July or August, which are known as the "dog days" of summer.) Dog-day cicadas are larger; they are black with greenish wings. Brood X cicadas are brown with clear wings with orange veins. Most notably, they have protruding red eyes. They're 1-1/2 to 2 inches long.
But how does an insect count up to 17? No one has figured that out yet. Researchers started naming and counting the broods in the late 1800s, and the 17-year cicadas have come out like clockwork ever since. They are the longest-lived insects in the world.
Weeks before they emerge, cicada nymphs dig exit tunnels to the surface. The insects have spent about 16 years and 11 months underground, sucking on tree roots for food. The exit tunnels are about 1/2 inch in diameter. Sometimes they take the form of little mud chimneys. When the ground temperature reaches 64 degrees F., the cicada nymphs emerge. At dusk, the nymphs make their way up the nearest vertical surface. That will most likely be a tree, but it could be a house, a lawn chair, or the family barbecue.
Overnight, the nymphs transform into adult cicadas. They molt (break out of their skin) and emerge as adult cicadas with wings, only they're white and soft. Their exoskeletons (outer shells) need time to darken and harden. Soon they turn brown. Then the adult cicada flies up into the trees.
Within a few days the male cicadas begin to sing as loudly as they can to try to attract a mate. Only the males sing or hum or scream, so if you pick up a cicada and it's silent, it's a female. This "singing" is created by a vibrating pair of tymbals, special membranes on the male's body.
Once the adults emerge, it's like a race to the finish. There are so many cicadas that predators - including birds, snakes, squirrels, raccoons, cats, dogs, even fish - gorge themselves. They eat until they can't eat any more. The cicadas that don't get eaten mate and lay eggs. That may be the secret of the massive hatchings of cicadas: Predators eat their fill, and there are still enough insects to continue the species.
After mating, female cicadas cut slits in twigs or branches of trees and lay their 400 to 600 eggs in batches of 20 or so. The adults die soon after mating and laying their eggs. The entire adult population of cicadas may be gone four weeks after they emerged. (This is when the streets and sidewalks may be littered with the crunchy bodies of the insects.)
Six weeks later, the eggs hatch and cicada larvae drop to the ground and burrow into the soil, eventually reaching the depth of about 12 inches.
For the next 17 years they tunnel around, sucking on tree roots for nourishment. (Adult cicadas don't eat solid food, but they do get some moisture from plants using their strawlike mouthparts.)
Dr. Gene Kritsky, a professor of biology at Mount St. Joseph College in Cincinnati, Ohio, is probably the country's expert on Brood X cicadas. He loves these bugs.
"Cicadas aren't pests," he says. "They don't eat anything and do minimal damage to trees - in fact, they act as 'nature's pruners.' " Branch tips may turn brown and fall off, but healthy mature trees respond by putting out new growth. Professor Kritsky advises people to get into the spirit of the event and celebrate the Brood X cicada, the way Cincinnati does. "Emergence is being embraced," he says. The city is putting out a CD to honor them - including a track of loud cicada songs donated by Kritsky.
It seems as though you're either going to like the emergence or you won't. Not many people are ambivalent about periodic cicadas. Kritsky says that his wife collected and filled an aquarium with cicadas during the last Brood X emergence. She was 7 at the time.
"I lead an exciting life," Kritsky muses. "At least once every 17 years."
• For further information:
Sorry for the long URL, but the University of Michigan's Museum of Zoology has excellent background information and photos in an easy format.
Log on to the 'Cicada Mania' site for updates on Brood X. Click on 'Are they coming to your town?' for a chart showing when and where named broods of cicadas are due to emerge.
Cicada expert Gene Kritsky's website has photos and sounds of cicadas.
Periodic Cicadas are not locusts. Locusts, which can swarm across farm fields and eat everything in their path, are a type of grasshopper. (Early American settlers, seeing the mass emergence of the cicadas, thought they were the locusts of the Bible.) These are smaller, slower cousins of the 'dog day' cicadas that drone in late summer. ('Dog day' cicadas spend part of their lives underground, too, but only a few years.)
Periodic cicadas cannot hurt you. Their mouths are only good for drinking, so they can't bite - or damage plants by eating them. They have no stingers, either. The only things at risk from the cicadas are young trees and greedy animals. Young trees may be damaged by egg-laying females. Cats and dogs might gorge themselves on the insect feast and get indigestion. At-risk trees can be covered with mesh cloth for protection. Pets need to be supervised so they don't overindulge.
After they mate and lay eggs, cicadas die. Their bodies may be icky to step on, but because they are rich in nitrogen they also enrich the soil.