Thursday, May 12, 2011

Emergence of the “Great Southern Brood” coming to Illinois

Emergence of the “Great Southern Brood” coming to Illinois

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Whether you anticipate it with pleasure or dread, there’s a large-scale natural phenomenon headed our way in the weeks to come, an emergence of 13-year periodical cicadas.

The insects in question are part of a group designated Brood XIX (19), or “The Great Southern Brood.” It occurs over a greater geographical range than any of the other 13- or 17-year cicada broods, with activity in 14 states anticipated. Like other year-classes of periodical cicadas, which, for the record, occur only in eastern North America, Brood XIX is composed of individuals representing three or four closely related cicada species.

Individuals from Brood XIX first began emerging in South Carolina in the third week of April, and they have now been reported aboveground in at least eight other states across the South and as far west as Oklahoma. The emergence of periodical cicadas seems to depend on soil temperatures reaching 64 ˚F, so it progresses from south to north with the season.

The current generation of the Great Southern Brood hatched from eggs laid in tree branches in the summer of 1998. As tiny nymphs, no bigger than small ants, they dropped to the ground and burrowed in. There they have been feeding on tree roots, and undergoing a five-stage development in anticipation of their turn at life on the wing. When the time is right, they will travel to the surface by way of a self-excavated tunnel and crawl up a tree, or whatever other vertical object happens to be nearby. There they will shed a nymphal skin one last time. [Photo: An adult periodical cicada newly emerged from its nymphal shell. John H. Ghent, USDA Forest Service,]

Periodical cicadas live as adults for only a few weeks, during which time they are interested in two things: feeding and reproduction.

Cicadas feed on the watery part of plant sap from trees and shrubs, which they extract by means of piercing-sucking mouth parts. Their feeding does not normally damage plants, since they remove only very small quantities of fluid and they do no significant damage to get at it. Since cicada mouths are designed to extract liquid from plants, you can rest assured they won’t bite people or other animals.

Of course, people and other animals will bite cicadas. The long list of creatures that eats them includes spiders, snakes, birds, dogs and more. If you stop to think about it, what small- to medium-sized animal that’s not strictly a plant eater would pass up such a bounty? As for people eating periodical cicadas, well. Historically, some groups of American Indians are reported to have eaten them (I haven’t been able to find whether they still do), and every emergence brings out recipes for them in newspapers and on the Web. I’ve never tried them, but I have to admit I’m intrigued—maybe this year.

Whether I eat them, you eat them or we and all the other predators eat them, enormous numbers from this year’s Brood XIX emergence will survive to accomplish the primary task of adult cicadas, reproduction. (And that’s precisely the point of their highly synchronized life cycle; scientists call it “predator satiation.”)

The males will entice mates with their long, loud song, often singing together in great congregations for an amplified effect. The females, once they have mated, will create a small slit in a branch, where they will lay their eggs, 400 to 600 of them. Egg-laying is really the only aspect of cicada behavior people might want to take precautions against, and only where cicadas turn out to be concentrated, since very young trees and shrubs may not tolerate the damage to small branches it involves. In such cases, cloth netting can be used to exclude cicadas.

Otherwise, the emergence of Brood XIX should be a great occasion for engaging the weird beauty of the life that surrounds us.

For more about Brood XIX and other periodical cicadas, check out