Update: We've added Allison Crawford's conversation with University of Kentucky Entomologist Doug Johnson, which aired on Sounds Good May 28, 2015
Cicada song is strong across the region this year as a brood of cicadas emerges after 13 years of sucking sap from tree roots.
University of Kentucky Entomologist Doug Johnson says there are 30 groups of periodical cicadas which emerge on either 13 or 17 year cycles, referred to as broods. Groups of cicadas emerge at different times to keep mating within their own brood. Despite living 13 years underground, the noisy insects are only above ground for about 4 weeks to molt and reproduce.
Johnson said periodical cicadas like these exist only in the eastern half of the United States, and this year’s brood is found only where there were trees 13 years ago.
“You’ll find that there’s a lot of land that may have had periodical cicadas 13 years ago but they don’t have any trees any more for some reason, a buildings been built on it, a road has been built through it,” Johnson said. “So they’re usually scattered in small locations around because humans have altered the form of the landscape.”
The insects are generally not a pest to farmers but they can cause damage to ornamental plants and young fruit trees, according to Johnson.
“If they come out in a year when young trees are set for example and they reproduce and their eggs hatch and fall to the ground, then those nymphs are going to live on the roots of those trees for the next 13 years. Now, because they’re a fruit bearing tree, they have actually a load on their system, a large number of cicadas could cut down on fruit production,” Johnson said.
Female cicadas cut into living tree branches to lay their eggs, which Johnson said can cause trees to lose about a year’s worth of growth. Cicadas have hardly any impact on wild trees.
Johnson said cicadas make their chirping noise by moving or rubbing together parts of their body. The name of the noisy critter is cicada, but they have been known by another name.
“Traditionally there are a lot of very poor names applied to them. In the U.S., probably the most common was locust. Locusts are actually grasshoppers and they don’t have anything to do with cicada. But if you reach back to your grandparents, they would have called these 13 year locusts,” Johnson said.
This brood of cicadas last emerged in 2002.
