Mapping millions of cicadas

A research team from the laboratory of Chris Simon, professor of ecology and evolutionary biology and a leading expert on periodical cicadas, is mapping the emergence of “Brood XIII” of the insects in the Midwest for the National Geographic Society.

Periodical cicadas only occur in the eastern half of the U.S. This is the first time that GPS has been used in combination with computerized data entry to accurately track the spectacle of a brood of periodical cicadas emerging.

Brood XIII, which was named by a U.S. Department of Agriculture entomologist in the late 1800s, extends from the northern half of Illinois to Iowa, Indiana, Michigan, and Wisconsin.

The cicadas in this emergence hatched in 1990, when their parents came up from under the ground.

The Simon lab research team is led by research associate John Cooley. On one of the first days of the Brood XIII’s emergence, he told the Chicago Tribune that more than 100,000 cicadas surrounded a single tree in a forest preserve in suburban Chicago.

Periodical cicada broods usually take about two weeks to emerge from the ground, depending on temperatures.

The periodicals, which differ from the less numerous, shorter-lived annual cicadas, live underground as nymphs for 17 or 13 years. There they feed on the roots of plants. When they come out, they finish maturing, mate, lay eggs in the twigs of trees, and die, leaving a litter of shells behind. The eggs hatch, the nymphs fall to the ground, and the cycle begins again.

During their brief time above ground, they dominate the landscape. They coat the trees and their shells coat the ground. Their synchronized, dawn-to-dusk buzz (a common sound effect in horror movies) is so loud that biologists counting them often wear ear protection.

The sight and sound of the periodicals was eagerly awaited by the Simon lab research team. They packed their cars with tents, GPS units, and collection supplies, and waited, “ears to the ground,” as Cooley said, for the first reports of the insects showing up around Chicago in late May and early June.

The maps they make of this emergence will help biologists understand more about the range of this species, where it will re-emerge in 2024, and how its distribution is affected by other broods that emerge in different years.

Simon, whose work is funded by the National Science Foundation, is interested in the DNA of the periodical cicadas, their evolutionary tree, and how new species form. Periodical cicadas provide a window into the speciation process.

Two members of her research team, Cooley and David Marshall, have studied the songs of cicadas to help differentiate new species that have formed relatively recently in evolutionary time, Simon says.

For more information about cicadas, go to Cicada Central at http://hydrodictyon.eeb.uconn.edu/projects/cicada/cc.html , a Web site maintained by the Simon lab research group.