Periodical Cicadas in 2007
Something not seen since 1990 is expected to reappear this year, said a University of Illinois Extension horticulture educator.
“This spring, the Northern Illinois Brood XIII of the 17-year periodical cicadas will make another appearance in northern Illinois,” said Ron Wolford. “The cicadas are expected to emerge north of a line from northern Iroquois County on the east, dipping southward to northern Sangamon County in the center of the state, and then rising northward to Moline and other Quad Cities on the west. This includes the Chicago area.”
On average, emergence numbers could total over 133,000 cicadas per acre. In the past, some emergences have had as many as 1.5 million cicadas per acre.
“The timing of emergence is determined by soil temperature,” he explained. “Abnormal springtime weather can delay or accelerate the timing of emergence. What causes them to emerge in a specific year is not well understood.”
Full-grown brown, 3/4-inch long periodical cicada nymphs will emerge this spring in late May. An indication of emergence is a series of soil chimneys that can be three inches high and 1/2-inch in diameter. They will also emerge through 1/2-inch diameter exit holes.
“The nymphs will burst out of the chimneys and holes around sunset and crawl up trees and shrubs,” he said. “Their skins will split down their backs and the adults will emerge.
“The adults are short-lived. Their main purpose is reproduction. Adult periodical cicadas are 1-1/2-inch long, black insects with protruding red eyes. Their clear wings have bright orange veins.”
About a week after emergence, the males will congregate and start singing to attract females. Females do not have sound-producing membranes like the male. The trilling is very loud and occurs during the sunny part of the day. The mating period lasts for two weeks, the males die, and the singing ends. The females will lay eggs for three to four weeks. The eggs are inserted into tree and shrub stems that are up to 1 1/2 inches in diameter. A female can lay more than 600 eggs.
“The eggs will usually hatch in mid-summer about six to ten weeks after egg laying,” said Wolford. “After hatch, the new nymphs will drop from trees and shrubs and dig underground to find roots for feeding for another 17 years.”
Even though periodical cicadas look a little scary, Wolford said they are not dangerous to humans or pets.
Heavy egg laying in newly-planted trees can cause twigs to break with leaves dying. Newly-planted trees can be covered with nylon netting tied around the trunk, but even trees with damage may just be a little bushier.
“All that effort may not be worth it,” he said. “The best control is to not plant trees the fall and spring prior to a predicted emergence in areas with a history of heavy emergence in the past. Mature trees, even when covered with cicadas, will show little damage.”
Wolford recommended sitting back and enjoying this wonder of nature. “It won’t occur again until 2024,” he said.
For more information on periodical cicadas, he recommended U of I Extension’s website "Cicadas in Illinois.”