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13-year cicadas emerging over next several weeks

May 5, 2011

By COLLEEN MCCARTHY
sdnreporter@yahoo.com

Northeastern Mississippi is already ringing with the drumming sounds of the periodical cicada Brood XIX, emerging for the first time in 13 years.
Brood XIX, or Brood 19, is an enormous group of four different species of cicadas, spread over much of the central United States. These cicadas are different from the large green ones you might see every year. These periodical cicadas are black and orange with red eyes will come out in the thousands over the next few weeks. The four species vary slightly in physical appearance, but they each have a distinctive “song” to attract females.
Brood XIX cicadas have already reportedly emerged and stick around until early to mid-June to mate before dying off.
Scientists know that cicadas come out when the ground temperature reaches 64 degrees. But how do they all know to stick to this 13 year cycle? Well, scientists aren’t really sure.
“We don’t really understand why, but we think that they just have this biological clock,” Blake Layton, an extension entomology expert, said.
In fact, there are other broods located farther north that emerge on a 17-year cycle. They are identical in physical appearance and behavior to many species in the 13-year broods, but for whatever reason, emerge on a different schedule and are considered a “sister species.” There are three separate broods of 13-year cicadas, and Mississippi will see the other two come in 2014 and 2015, respectively.
One of the most noticeable signs that the cicadas have arrived are the brown, empty shells they leave behind. Layton explained that all insects shed their “skins” in this manner as they grow, the same way a child grows out of a pair of shoes.
“Insects have external skeletons, and after a while it gets too tight for them,” Layton said. “Once they shed their skin for the last time, which is the ones we see stuck to trees and such, they become adults.”
Layton estimates that Oktibbeha County will likely see tens of thousands to hundreds of thousands of cicadas per acre. The cicadas emerge in the billions as a survival strategy. They are a popular treat for birds, reptiles and mammals, but there are just too many for predators to eat.
“They catch predators by surprise by all coming out at once,” Layton said. “Sometimes you’ll have a few that come out too early, but they rarely survive to reproduce.”
Swarms will likely become a common sight over the next few weeks, but do you need to worry about your gardens and trees?
Not really, Layton said. Adult cicadas barely eat at all after stuffing themselves on tree sap as nymphs underground for the last decade or so. Female cicadas do lay their eggs inside the twigs of hardwood trees, which generally causes those twigs to turn brown and die. But this merely provides a “pruning,” and won’t cause major damage to most trees. Young fruit or ornamental trees may be at risk, but a net on the tree would provide sufficient protection.
The Brood XIX cicadas will continue to emerge over the next few weeks. They will mate and lay their eggs, and die off in June, just in time for the annual cicadas to emerge. From their eggs will come little nymph cicadas, who will fall to the ground, burrow in and stay there until 2024.

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