Note: The Chicago area won't see the 17-year cicadas until summer 2024. The 17-year cicada emerges in different geographic areas on differing schedules. These different emergence areas are referred to as Brood areas. Brood X (the Great Eastern Brood) is emerging in 2021 in four counties in central eastern Illinois (Edgar, Clark, Crawford, and Vermilion).
The periodical cicada (Magicicada), is a native North American insect species inhabiting the eastern United States and, according to Penn State University, is found nowhere else in the world.
Cicadas are often mistakenly referred to as locusts. Locusts are members of the grasshopper family, which have chewing mouthparts; cicadas have sucking mouthparts and do not chew. Periodical cicadas will not bite. They have been known to land on people, but they cause no harm. Even though adult cicadas suck on plants for nutrition, they feed very little as adults.
Periodical cicadas are not the same species as annual cicadas. Even though annual cicada nymph development cycles are also very long and variable, they are not synchronized like the periodical cicadas. Annual cicadas mature at different times, which is why we see them each year. Annual cicadas are green with black and are also larger than periodical cicadas, approximately 1½ to 2½ inches in length, and appear from July to September. Periodical cicadas are black with orange wing veins and red eyes, approximately ¾ to 1½ inches in length, and appear from May to July.
The life cycle of cicadas is a mystery to entomologists. Periodical cicadas require either 13 or 17 years in the nymph stage, developing underground, and mature very slowly. They are synchronized to emerge en masse, every 13 or 17 years. Their 17-year life span makes them the longest-lived insect known. There are two races of periodical cicadas, which are distinguished by the time required to develop into adulthood: the 17-year cicadas, which appear in the north, and the 13-year cicadas, which appear in the south.
The 17-year periodical cicadas last emerged in the Chicago region in 2007. Nymphs emerge from the ground when soil temperatures warm to approximately 64º F, usually sometime in May. They usually emerge from the ground after sunset, leaving behind very visible exit holes, and quickly crawl to any nearby vertical structure, preferably a tree or shrub. They shed their skins as they molt into adults, leaving behind their empty shells. Shortly after molting, their wings unfurl and their yellow-white skin darkens as their exoskeleton completely hardens.
Adults begin mating after they have completely matured, usually within a few days, and remain alive for approximately three to four weeks. Shortly after mating, females climb to living trunks, branches, and twigs, where they split the bark and deposit between 24 and 48 eggs. Adult females mate many times and are capable of laying up to 600 eggs during their lifetimes. Approximately six to ten weeks after eggs are laid, ant-like juveniles hatch and drop to the ground, where they burrow from a few inches to more than a foot into the soil. They remain underground as nymphs, feeding on tree and shrub roots for years.
Male cicadas will call females to mate by vibrating their tymbals, which are two rigid, drum-like membranes on the undersides of their abdomens. Different species of cicada produce different songs. Males respond to the calls of other males, creating a chorus of ‘singing’ cicadas that can be deafening. Females do not have tymbals and are incapable of producing the same sounds.
Damage to woody plants occurs primarily when females split the bark on small-diameter limbs and branches for egg laying. Healthy and larger-diameter trees and shrubs can easily heal the ½- to 1-inch slits; smaller ones often wilt and die.
Developing nymphs feed on plant roots underground, which can damage trees and shrubs by reducing plant growth.
Treatment & Solutions
Newly planted and small-diameter trees and shrubs can be protected with fine netting, cheesecloth, or row-cover fabric tied securely at the base, to keep nymphs from crawling up the trunks upon emergence, as well as preventing females from slitting bark to lay eggs.
Remove small, damaged branches to keep eggs from hatching and future populations low. Also, delay planting new trees and shrubs until adult periodical cicadas are gone, usually by mid-July.
The use of chemical sprays to kill adult periodical cicadas is not recommended. Using insecticides will also kill beneficial insects that feed on harmful insects and can injure natural predators such as birds, raccoons, skunks, and moles.
Cicadas are edible; they're even considered a delicacy in many countries, as well as in different parts of the United States. Some claim that cicadas are high in protein, but recent research conducted at the University of Cincinnati’s College of Engineering has determined that cicadas may contain high levels of mercury. Diners therefore are cautioned to limit their ingestion of these "delicacies" to just a few.