The cicadas are coming, the cicadas are coming!  

Can you hear them? Probably not yet, but soon, Illinois will be awash in the songs of periodical cicadas. This year (2024) is a big year for periodical cicadas in Illinois, where Broods XIII and XIX will be emerging throughout much of the state at the same time. This is the first time this has happened since 1803, and it won’t happen again until 2245! Despite some talk of an impending insect apocalypse, cicadas don’t pose a threat to humans (or pets), although that newly planted tree or shrub may be a different story.

While two broods will be emerging at the same time, they won’t be emerging in the same places. Brood XIII, also known as the Northern Illinois Brood, will be emerging in the northern half of the state. Brood XIII contains all three species of 17-year periodical cicadas: Magicicada septendecim, M. cassini, and M. septendecula. In addition to Illinois, this brood will be emerging in Indiana, Iowa, Wisconsin, and possibly Michigan.

Brood XIX, also known as the Great Southern Brood, will be emerging in the southern half of Illinois. The four species of cicadas in this brood are 13-year cicadas: Magicicada tredecim, M. neotredecim, M. tredecassini, and M. tredecula. This brood is the largest of the 13-year broods, geographically speaking, and will emerge across Alabama, Arkansas, Georgia, Illinois, Indiana, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, and Virginia.

There may be a few places in central Illinois, around Springfield, where the two broods will be emerging in the same area. However, they aren’t expected to overlap to any great extent.

In addition to Broods XIII and XIX, there may be some cicadas from Brood XXIII, the Mississippi Valley Brood, that may emerge. This brood will emerge in 2028, but occasionally, some periodical cicadas will emerge four years early, which in this case would be 2024, and are referred to as stragglers. If any stragglers from Brood XXIII do emerge it will be primarily in far southern Illinois. 

Periodical cicada life-cycle and biology

Periodical cicadas are among the longest-lived insects on the planet, living for 13 or 17 years. They spend the vast majority of that time living underground, feeding on tree roots. Once the soil warms enough in the spring (64°F at 8 inches deep), they will begin to emerge, depending on where you are located, sometime in May or early June. The nymphs usually emerge from the soil in the evening and will climb up trees or other objects and molt, leaving behind the familiar cicada ‘shells’ (shed exoskeleton).

After the adults emerge, they are white, soft, and squishy but will darken and harden overnight. Contrary to popular belief, adult periodical cicadas do feed on plants (usually woody plants). However, they will spend most of their time above ground reproducing.

Male cicadas will start singing four or five days after they emerge. They will gather in trees and sing together to attract females. Females lack structures to produce sound (tymbals), so only males will sing. Each species of cicada has a distinctive song they produce.

After mating, female periodical cicadas will lay their eggs in the new growth of woody plants. They prefer branches that are about the width of a pencil or a little larger (up to ½ inch or so in diameter). They will use their saw-like ovipositor (egg-laying organ) to cut into branches and lay 10-20 eggs before moving further down the branch. In total, each female will lay around 500-600 eggs.

After about a month, the adult cicadas will begin to die. Large piles of cicadas can accumulate under trees and can smell rather unpleasant (similar to roadkill). However, their decaying bodies will serve as fertilizer for plants.

Six to ten weeks after they are laid, the eggs will begin to hatch. The tiny cicada nymphs will drop to the ground and begin feeding, often on grass roots. Over time, they will dig down into the soil, 8-12 inches deep, and feed on tree roots for the next 13 or 17 years.

Source: extension.illinois.edu