They're back! This is the year the periodical cicadas (a.k.a., periodical "locust" and 17-year cicada) will reappear above ground in a small portion of east-central Iowa. After living as nymphs underground since 1990, this is the year they transform to noisy, winged adults to emerge in June for a brief moment in the sun. Then they will disappear back in the ground where they will stay until 2024. Amazing.
The periodical cicadas are expected in 12 east-central counties (see the accompanying map). They will not be everywhere within those counties, however. Previous experience with this emergence (called Brood XIII) indicates the cicadas will be very spotty. You might have to check around to see this spectacle of Nature. The most likely places for these unusual insects are in large, long-standing, upland native woodlands.
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 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 long-term 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 the year for eastern Iowa! Don't miss this opportunity. The next emergence anywhere in Iowa will be the large central Iowa Brood III that will be back in 2014!
Solid: Counties where periodical cicadas were reported in 1990. Speckled: Counties where periodical cicadas were reported prior to 1990 but not in 1990.
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