Each year, somewhere in the United States east of the Rocky Mountains, a brood of the periodical cicadas (Magicicada septendecim) emerges. Periodical cicadas have two distinct races based on required time to complete their life cycle: a 17-year northern race and a 13-year southern race. In each race there are three distinct species. The 17-year periodical cicada is the most common and longest-lived of this insect. The northern third of Illinois is in the range Brood XIV, which last appeared in 1990. Its next appearance is due in 2024.
The annual cicadas are green to black in color with transparent silvery wings and are nearly double in size to the periodical cicadas. They appear each year from July to September. The black eyes of the annual cicada distinguish them from the red-eyed periodical cicada. Both types of cicadas are harmless to humans except their sound may be a minor nuisance.
Adult cicadas have sucking-piercing mouth parts. They do not feed on leaves, and if they feed at all, it is by sucking sap from young twigs. The principal damage suffered by trees and shrubs results from egg-laying by the adult female. The damage is confined mainly to smaller twigs and branches. As many as 600 eggs are laid in numerous, small, elongate slits made by means of a long, knife-like ovipositor. Heavily damaged twigs and branches may wilt and break off. Some injured branches may not die the first year, but the wounded area is a weak site on the plant and may eventually break off in a wind storm. Oak, hickory, apple, peach, and pear trees are the most seriously damaged species, while pines and spruces are rarely injured. Because this is a unique North American insect and our native species have evolved together, older, mature, native trees are not seriously damaged by the egg-laying.
The eggs hatch in six or seven weeks. The nymphs fall to the ground and burrow into the soil, seeking suitable roots to attach their piercing- sucking mouth parts. The cicada nymphs suck sap from roots until the last year of their life cycle. After completing the seventeen-year cycle, the full-grown nymphs make their way up to the surface where they crawl up a convenient vertical object such as a tree trunk. The outer covering of the nymph splits open, and the winged adult emerges, leaving behind the hollow skin casing. The adult cicada lives for 20-25 days.
Since cicada damage could delay re-establishment of new transplants, avoid planting very small trees in an area where an emergence is soon expected. If small trees are planted, protective measures should be exercised. Cover the branches of small trees, 2" or less in diameter, with fine netting, such as cheesecloth, during the egg-laying period. Secure the netting to the trunk in order to prevent the insect from getting inside the covering. Most evergreens, such as pines and spruces, need not be protected, since the cicada does not lay eggs in their branches.
Research has shown insecticides may kill adult cicadas but will not harm deposited egg masses. Since cicadas are a desirable food source for many animals and birds, chemical spraying is not recommended.