This is the year! After waiting in the soil for 17 summers, that is, since the summer of 1980, the periodical cicadas will again appear in a significant portion of the state of Iowa.
The periodical cicadas (a.k.a., periodical "locust" and 17-year cicada) are expected in 46 central, south-central and south-east counties (see the accompanying map). They will not be everywhere within those counties, however. The most likely places for these unusual insects is in large, long-standing, upland native woodlands.
Although this is our largest brood of periodical cicadas, it is not the only brood in the state. Other recent periodical cicada emergences occurred in northeastern Iowa (1990) and southeastern Iowa (1985). The current emergence (called Brood III) will occur in Iowa, Missouri and Illinois. Other broods occur in other years in other parts of the eastern United States.
Special features. Four characteristics of the periodical cicadas make them exceptional even by the standards of the incredible and fascinating world of insect species. The first is the 17 year life cycle. The life span of 17 years puts the periodical cicadas among the longest-lived insects in the world. All but a few weeks of those 17 years are spent as a nymph, 18 to 24 inches deep in the soil of wooded and forested areas, feeding on sap from tree roots.
The second phenomenon is how all the cicadas in an area emerge at once in highly synchronized fashion. The nymphs develop slowly and at different rates, but at the end of the 17 years, they have all developed fully and begin digging their way to the soil surface.
The nymphs surface 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 adults laboriously emerge over the course of about one 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.
The third special feature of periodical cicadas is the incredible noise for which they are known. The males "sing" with a loud buzzing or drumming sound that goes on all day long. The incessant buzzing sound is produced by 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 to control sound volume and quality and the upward angles of the wings form a megaphone-like chamber that further controls the sound.
And finally, periodical cicadas can occur in numbers that stagger the imagination and repulse the squeamish. Populations can reach up to a million and a half cicadas per acre. That can mean as many as 40,000 cicadas per tree.
Witnessing a massive emergence of periodical cicadas takes patience and planning but is worth the wait. This is our year! Don't miss this opportunity because your next big chance will be in the year 2014!
(See also the 17-year cicada pages .)
This article originally appeared in the May 9, 1997 issue, pp. 66-67.