With all the media frenzy around this year’s upcoming cicada emergence, what can we really expect? Let Extension help you separate fact from fiction.
Why do they live so long?
Cicada larva (or grubs) spend most of their life underground, feeding on tree roots. Depending on the species, this can be anywhere from two to 17 years! Scientists aren’t sure why they live so long. A current hypothesis is that it’s a way to avoid synching their lifecycle with predators. In other words, outlive the things that want to eat you! But how do they know 17 (or 13) years have passed? Scientists don’t know that either. One theory is that they have an internal molecular clock that picks up on environmental cues such as the seasonally changing composition of the sap in the tree roots. After enough time has passed and the soil begins to warm, they make their way back to the surface, molt, and take on their new winged form. And another note: cicadas are not locusts. While this misnomer has persisted for hundreds of years, locusts are more closely related to grasshoppers.
When can we expect them?
Despite what you may have seen in the media, northern Illinois will only be seeing one brood of 17-year cicadas. The 13-year brood that also emerges this year will be seen further south. You would have to visit Coles, Douglas, or even Champaign Counties to see the dual emergence. So, for those of us in northern Illinois, this will be an ordinary cicada year. Cicadas emerge when the soil temperature reaches 64 degrees F, eight inches below sod. Historically, this has occurred around the second or third week of May. Last year, it was May 24. In 2022, it was May 12. Currently, as of April 3, 2024, the soil temperature is in the mid- to upper-40s here in northern Illinois, so we still have a way to go. Despite the fluctuating temperatures we’ve seen this winter, we’re still trending similar to previous years at this time (Data provided by the U of I Water and Atmospheric Resources Monitoring Program.)
How can we prevent damage to plants?
Adult cicadas do not eat very much, so there is no risk of feeding damage to either trees or non-woody plant species. The main source of damage is from the slits in the small outer branches in which females lay their eggs. In older, more established trees and shrubs, this damage will be minimal, and some trees may even benefit from this natural form of pruning. For smaller, newly planted trees and shrubs, one option to protect them is to cover them with fine netting (less than ¼-inch holes) or tulle. Cover the outer branches and secure the netting at the trunk near the ground. Pesticides will not do much to control populations and are not recommended for use.
So, enjoy this wonder of nature! If you like bugs, plan a trip south to see the once-every-221-year dual emergence or try one of those cicada recipes that will soon be popping up online (but only if you’re not allergic to shellfish!).
Want to learn more?
Join me for a free presentation to learn more about this winged creature’s history, lifecycles, and what effect they may have on plants and our lifestyle throughout Illinois. Two locations still have seats left: April 16 in St. Charles at go.illinois.edu/CicadasKaneCounty or April 17 in Yorkville at go.illinois.edu/CicadasKendallCounty. For more information on cicadas, you also can check out the University of Illinois Extension’s factsheet.
About the author: Jamie Viebach is the University of Illinois Extension Horticulture Educator serving DuPage, Kane, and Kendall counties. Viebach’s primary areas of expertise are native plants, landscaping, pollinators, and rain gardens.