The Magical Screaming Cicadas
Photos by the author.
June of 2021 the residents of four east central Illinois counties (Clark, Crawford, Edgar and Vermilion) were treated to a truly wonderous experience—the emergence of the 17-year periodical cicadas known as Brood X. There are two cycles for periodical cicadas: 13-year and 17-year, which spend most of their lives as larvae underground. They emerge en masse for four to six weeks, brilliantly orange-colored with red eyes, screaming and ready to breed. One would think their coloration and noise would attract predators, and it does. However, this strategy, known as predator saturation, confuses predators which consume the cicadas. The cicada numbers overwhelm the predators ensuring enough remain to breed and lay eggs.
The 17-year cicadas have the longest lifespan of any insect. Eggs are laid in the limbs of young trees individually and in rows. Oaks and maples are favored, and young trees can be covered with netting to protect them from damage in high infestation areas. The eggs hatch and the young fall to the ground and dig underground where they subsist on root sap. Several weeks before emerging, exit holes are excavated and they wait for the right soil temperatures before coming up for their final molt to adulthood.
There are 20 species (eight genera) of cicada in Illinois. Periodical cicadas belong to the genus Magicicada or “magical cicada.” The other seven genera are called annual cicadas; though they can be seen most years, they, too, spend an extended period of two to nine years underground. Annual cicadas often have greenish wings compared to periodical cicada’s bright orange wings. Cicadas are also grouped based on whether their percussion mechanism, the tymbal membrane, is concealed, as in most large annual cicadas, or exposed in the periodic and prairie cicadas. Exposed tymbal cicada adults are generally smaller (around 1 inch) and present earlier in the season, between late May and early July. Concealed tymbal species are closer to 2 inches in length and occur from July to September or October.
One of the loudest insects in the world, only cicadas possess this true tymbal percussion mechanism. The tymbal, like surface of a drum, is vibrated and the sound echoes within air-filled abdomen of male cicadas. Only the songs of males are audible to human ears. The acoustic signals of males are used to identify cicada species. If you would like to learn more, those living in northeastern Illinois can participate in cicada acoustic surveys (singinginsects.net). Recordings of the calls of various cicada species, along with additional information on signally insects is also available online (insectsingers.com).
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Eaton, E.R., and K. Kaufmann. 2007. Kaufman field guide to insects of North America. Houghton Mifflin Co. New York, NY 392p.
Marshall, S.A. 2006. Insects, their natural history and diversity with a photographic guide of Eastern North America. Firefly Books Ltd. Buffalo, NY 732p.
Strang, C.A. 2018. Singing insects of the Chicago Region: a guide to crickets, katydids, grasshoppers, and cicadas with audible display. Chicago Wilderness. 115p.
Angella Moorehouse has worked for the past 25 years as a field biologist for the Illinois Nature Preserves Commission in west-central Illinois. She specializes in plant and insect ecology with a focus on using photography to document plant-pollinator interactions.