Billions Of Dead Cicadas Will Smell Like Roadkill, Linger For Weeks

ILLINOIS — The cicadas aren’t done with Illinoisans yet. Even in death, the billions of bugs that rose from the ground earlier this spring to unleash their defeaning mating calls will continue to make themselves known.

“After about a month, the adult cicadas will begin to die,” according to the University of Illinois Urbana-Champaign’s Illinois Extension. “Large piles of cicadas can accumulate under trees and can smell unpleasant, similar to roadkill.”

The odor typically lasts a couple weeks, according to the Morton Arboretum, but there is an upside.

“Cicadas are a fine addition to the compost pile,” Stephanie Adams, the arboretum’s plant health care leader, said in a blog post, which noted that it’s important to mix the insects with green and brown plant material, keep everything moist and turn it often. “An unturned pile of dead cicadas will stink more.”

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This spring was particularly prolific for cicadas in Illinois. In a rare event that hasn’t happened since 1803, the emergence timelines for Brood XIII, known as the Northern Illinois Brood, and Brood XIX, or the Great Southern Brood, aligned.

Cicadas spend most of their lives underground as immature nymphs but surface en masse every 13 or 17 years. Their extraordinarily long life cycle, the longest of any insect on the planet, is part of an evolutionary strategy that has allowed the species to survive for 1.8 million years, or from the Pleistocene Epoch.

After mating, female cicadas lay eggs in the branches of new growth, according to Illinois Extension. The eggs hatch in about six to 10 weeks, with the nymphs dropping to the ground and gradually digging several inches into the soil, where they feed on tree roots for well over a decade, until their next emergence.