Cicadas, with their distinctive songs and synchronized appearances, are a fascinating natural phenomenon. These insects spend years developing underground before emerging in large numbers.
The Double Emergence Event
The year 2024 marked a rare occasion for Illinois, as two distinct cicada broods emerged simultaneously. This event involved Brood XIII, a 17-year periodical cicada, and Brood XIX, a 13-year periodical cicada. Their synchronized appearance had not occurred since 1803 and is not expected to happen again until 2245.
Brood XIII, the Northern Illinois Brood, last emerged in 2007. Brood XIX, the Great Southern Brood, last emerged in 2011. While both broods emerged in the same year, they generally occupy different geographical ranges, meaning most areas experienced the emergence of only one brood.
Where to Expect Them in Illinois
Illinois was a primary location for this dual emergence, though the two broods were largely separated geographically. Brood XIII emerged primarily in northern Illinois, extending into areas like the Chicago metropolitan region. This brood’s distribution also included parts of southern Wisconsin, eastern Iowa, and a narrow strip of Indiana.
Brood XIX, the Great Southern Brood, appeared across southern and central Illinois. This brood has a broader geographic reach, spanning many states across the southeastern United States. While the broods generally did not overlap significantly, a thin zone in central Illinois, including counties such as Macon, Sangamon, Livingston, and Logan, experienced the presence of both.
Understanding Periodical Cicada Life Cycles
Periodical cicadas have remarkably long and synchronized life cycles. They spend almost their entire lives as nymphs, burrowed underground, typically 8 to 12 inches deep. During this subterranean period, they feed on xylem fluids, which are nutrient-rich liquids drawn from the roots of trees and woody plants.
The emergence of these nymphs is triggered when the soil temperature at an 8-inch depth reaches approximately 64 degrees Fahrenheit. Once this temperature threshold is met, the nymphs construct exit tunnels and ascend to the surface. Their adult lives are brief, lasting only about four to six weeks, focused on mating and egg-laying.
What to Anticipate During Peak Emergence
During a mass cicada emergence, the most prominent change is the sound. Male cicadas produce loud mating calls using specialized organs on their abdomens. This collective buzzing can reach volumes between 90 and 100 decibels, comparable to a motorcycle or subway train.
Despite their large numbers and loud presence, periodical cicadas are generally harmless to humans and pets. They do not sting, bite, or pinch. As they transition to their adult stage, they shed their nymphal exoskeletons, which can be found clinging to trees, shrubs, and other surfaces. Adult cicadas live for only a few weeks, after which their bodies decompose, returning nutrients to the soil.