After 17 years in wait, cicadas are rising: U.S. invasion starts in 5, 4, 3 . . .

AFP-JIJI, AP, The Washington Post

The hordes are rising. A cicada invasion is imminent in the United States, with millions of the large cricketlike insects beginning to emerge from the earth after 17 years lying in wait.

The first of the bugs that are expected to blanket the U.S. East Coast have already been spotted.

“The Brood II emergence has begun!” cheered the site cicadamania.com, where the subculture of insect fans can record sightings.

The onslaught will truly begin later this month, once the average ground temperature hits 17 degrees. At its peak, there could be swarms with between 1,000 and 2,000 chirping critters per square meter.

Although cicadas are common around the world, this cyclical phenomenon happens only in the eastern half of the United States.

Every 17 years, these “periodical cicadas” mature, mate, lay eggs and die in a deafening concerto.

Their offspring — which won’t be seen again for another 17 years — burrow into the ground, 20 cm deep, where they will feed on the sap from roots until their day in the sun arrives.

The broods — there are 15 of them — are classified by Roman numeral. Most are on a 17-year cycle, though three reproduce every 13 years and the cycles are staggered, meaning at least one of the broods hatches each year.

But not all broods are created equal, and Brood II is a big one. Experts don’t know for sure how many cicadas are lurking underground, but 30 billion seems like a good estimate. If they were lined up head to tail, they would reach the moon and back. At the Smithsonian Institution, researcher Gary Hevel thinks the total may be more like 1 trillion.

Over the next few weeks, they will emerge and launch a reproductive orgy when the larvae split their skins and mature into adult form, explained University of Maryland entomologist Michael Raupp.

“Then they’ll scramble in a flight to the treetops. The males will begin to court the females. They will mate,” he added.

The females will “lay their eggs, these eggs will hatch and will tumble down to the earth and feed again for another 17 years.”

The bugs, of the scientific order Hemiptera — which makes them true bugs — are about 2 to 3 cm long. They are called magicicadas, as in magic. They are black and have red eyes and translucent wings with orange veins. They don’t sting and only threaten the young trees they will pump for sap.

And they will be loud. The males sing to the females in a mating call created through their tymbal, an abdominal membrane. By the thousands, the chirp rises to a deafening roar.

Most of the cicadas will die quickly, preyed on by birds and small mammals.

“Adult cicadas are a huge source of food for various animals,” said Andrew Liebhold, Agriculture Department entomologist. “They are a very good source of nutrition and enhance reproduction of several species of birds and mammals.”

Raupp noted, “They are higher in protein and lower in fat than a steak,” adding he prefers them raw.

Why do they emerge only every 13 or 17 years? Some scientists think they come out in these odd cycles so that predators can’t match the timing and be waiting for them in huge numbers. Another theory is that the unusual cycles ensure that different broods don’t compete with each other much.

And there is the mystery of just how these bugs know it has been 17 years and time to come out, not 15 or 16 years. “These guys have evolved several mathematically clever tricks,” Raupp said. “These guys are geniuses with little tiny brains.”