Cicadas set to emerge in Kentuckiana in coming days

LOUISVILLE, Ky. (WDRB) -- While some sporadic sightings have begun to occur already, it's expected that by the end of next week, cicadas will be coming out in full force.

The Brood X variety of the periodical cicada will emerge after 17 years underground with a cacophony of mating calls before the cycle begins again a few months later.

In the bullseye of the emergence is the Louisville area and southern Indiana.

"The whole purpose of coming out of the ground at this time of year is to find mates and just repeat the cycle," said Steve Yanoviak, an insect ecologist at the University of Louisville. "They really want to get that over with and get down into the ground."

Billions will emerge from the ground to mate. Females will then lays eggs in the branches of trees.

"Females will lay their eggs in twigs of trees, a quarter-inch diameter — maybe a half-inch diameter — in twigs," Yanoviak said. "The nymphs, we call them — the juveniles — will drop into the soil and begin feeding on the roots of the trees."

The nymphs hatch about a week after they are laid.

The reason for why they hatchlings spend 17 years underground is largely a mystery but there are theories.

"There's also a 13-year periodical cicada and the number 13 and 17 are really important because they're both prime numbers," Yanoviak said. "There's been a fair amount of speculation that is very hard for predators to track a prey item that comes out at that frequency. There's really no multiple of it. So a predator, for example, that has a two-year life cycle, could track a cicada that has an eight-year life cycle. Every fourth generation, they'd be feeding on lots of cicadas."

The noise many people will hear comes only from the male cicadas, a mating call used to attract females.

There is no danger from the cicadas as they don't bite humans. However, younger trees could have damage from the females laying eggs in the limbs. Netting can be placed over vulnerable trees to protect them.

"They can be noisy if you're right by them, but that's more of a nuisance," Yanoviak said. "But really, aside from that, it's really something that we should collectively celebrate."