One of the most interesting insects of North America is the periodical cicada (a.k.a., periodical "locust" and 17-year cicada). Their life span of 17 years includes them among the longest-lived insects in the world. Periodical cicadas spend 17 years 18 to 24 inches deep in the soil of wooded and forested areas, feeding on sap from tree roots. Then, in a highly synchronized fashion, all the cicadas in an area emerge at once.
Cicada nymphs dig their way out of the soil during late May and June and climb up tree trunks, posts and poles. The outer shell of the nymph splits along the middle of the back, and the winged adult laboriously emerges in about an hour.
Each adult may live for 5 or 6 weeks. During that time the males and females mate and the females lay the eggs that are the start of the next generation. Eggs are laid into the small twigs of trees and shrubs. This causes moderate twig dieback and some disfigurement ("flagging") of forest and woodland trees, but no longterm consequences.
The eggs hatch after 6 to 7 weeks and the newly hatched nymphs fall to the ground, burrow until they find a suitable tree root, and begin the feeding and waiting that will last until the year 2014.
Periodical cicadas are well-known for the incredible noise they make when they emerge. The males "sing" with a loud buzzing or drumming sound that goes on all day long. With populations that can reach up to a million and a half cicadas per acre, the sound can be as deafening as it is incessant.
The cicada males sing by vibrating two shell-like drums located along the sides of the abdomen. Strong muscles vibrate the drum membranes several times per second. The resulting high-pitched, rapid clicks are resonated through air sacs and other structures to control sound volume and quality. The upward angles of the wings form a megaphone-like chamber that further controls the sound.
Periodical cicadas are found only in North America and only east of the Rocky Mountains. Witnessing a massive outbreak takes patience and planning but is worth the wait. Refer to the accompanying map for the expected distribution of Brood III in Iowa. Seeing an emergence of periodical cicadas is the "trill of a lifetime."
|This page part of the Iowa State Entomology site.
|Last updated June 19, 1997