When are the 17-year cicadas due to return to Chicago?
The 17-year periodical cicadas last emerged here in the spring of 2007 and will next return in 2024. Their long life cycle is genetically determined and weather is not a factor. Nymphs emerge from the ground in the spring of the 17th year when soil temperatures about eight inches below the surface warm to 64 degrees. In the Chicago area, this usually happens in late May or early June.
The 17-year life cycle of the periodical cicada makes it the longest-lived insect known. Adult female cicadas deposit eggs in the twigs of trees and large shrubs, after which, in six to ten weeks, newborn nymphs drop to the ground and burrow in for 17 years, feeding off the juices of tree roots.