RALEIGH — One the worlds largest and most unusual swarms of insects will invade portions of North Carolina and other states along the East Coast later this month when billions of 17-year cicadas emerge from their underground homes for a rowdy, monthlong mating spree.
The clock will start ticking for the cicadas of Brood II when underground temperatures reach 64 degrees. That means its time to date, mate and die all in less than four weeks.
This only happens in eastern North America, no place else in the world, said Clyde Sorenson professor of entomology at N.C. State University, of the periodic cicadas unconventional life cycle.
The party is already getting started in north-central North Carolina, the southernmost rim of the Brood II range, which extends northward through Virginia and as far north as Connecticut and New York. Cicada nymphs, as the insects are known before they grow wings and begin to fly, were spotted earlier this week in Chatham and Forsyth counties, Sorenson said. All brood members will emerge sometime between now and the middle of May and be gone before mid-June.
Cicadas live in North Carolina year-round, but the periodic types are easy to identify; they have big, black-and-orange bodies and bulgy red eyes. And they have a distinct whee-oh, whee-oh mating call. When encountered en masse, the sound could almost be mistaken for a spaceship landing in your back yard, Sorenson said.
You can determine when theyve started coming out just by driving with your windows down, he said.
For bug experts such as Sorenson and Bill Reynolds, coordinator of the Arthropod Zoo at the N.C. Museum of Natural Sciences, the four- to six-week-long appearance of periodic cicadas brings a welcome opportunity to learn more about these unusual insects.
Last brood seen in 2011
Periodic cicadas emerge only once every 13 or 17 years, depending on the species. One group of 13-year cicadas and two 17-year broods are found in North Carolina. The last seen here was Brood XIX, a 13-year cicada that appeared in 2011.
Magicicadas, as they are known scientifically, have an internal clock that tells them when its time to leave their lairs, fly into trees, and start a two- to four-week courtship ritual that involves loud screechy noises and line dancing or rather jumping from branch to branch to attract the attention of the opposite sex, Sorenson said.
The noises are created with a drum-like organ near their stomach known as a tymbal.
They pulse air through it with motions of the body, Reynolds said.
Between each call, the male cicada pauses in hopes of hearing a yes from a nearby female. If she responds with a clicking sound of her wing, the male drumming becomes faster and more rhythmic.
Males will couple up with as many females as possible during their time above ground, but a female typically finds just one mate before depositing her eggs into slits at the tips of tree branches, Sorenson said.
In time, the tips of the egg-bearing branches will fall to the ground, where the nymphs will dig in to stay for the next 17 years.
Aside from annoying humans with loud noises and pesky fly-bys, the only other negative impact of cicada activity is the potential harm to limb tips of delicate young fruit trees.
Ecologically, they are very beneficial, said Reynolds, who has been fascinated with cicadas since childhood.
They arent poisonous or venomous. A lot of things eat them: birds, lizards, fish, mammals like squirrels and field mice, even dogs and cats.
And when they die, their bodies provide nutrients to trees, plants and flowers in the forest, he added.
You could think of them as the largest single dose of fertilizer in the natural world, Reynolds said.
A call for restraint
For all these reasons, he urges people to exercise patience and refrain from bombing the cicadas with insecticides.
Not every acre within the habitat range will see large numbers of Brood II cicadas. Theyre drawn largely to forested areas that have been undisturbed since the previous emergence, the scientists said.
With development continuing at a busy pace in central North Carolina, there may be fewer Brood II members here this year than during their last visit. And fewer still the next time around but that wont be a certainty for another 17 years.