Cicada Season Arrival
Double Brood of Periodical Cicadas
This spring, prepare for an extraordinary natural phenomenon in the Midwest and Southeast: the simultaneous emergence of two cicada broods, Brood XIII and Brood XIX. Known as a “Double Brood,” this event is remarkably rare, occurring just once every 221 years
From late April to mid-May 2024, these regions will witness the arrival of trillions of these red-eyed, sonorous insects. Typically, the cicadas will be present for about four to six weeks, completing their life stages of growth, molting, and mating.
Geographic Distribution of the Double Brood
  • Brood XIII: Known as the Northern Illinois Brood, this 17-year brood appears primarily in northern Illinois, extending to central Missouri, southern Wisconsin, eastern Iowa, and northwestern Indiana.
  • Brood XIX: The Great Southern Brood, following a 13-year cycle, is found across parts of Louisiana, Arkansas, Alabama, Mississippi, Georgia, South Carolina, North Carolina, Tennessee, Missouri, Illinois, and Kentucky. Despite some overlap in Illinois, the densities of these cicadas will likely not double.
Cicada Types: Periodical and Annual
Cicadas are categorized into two types: periodical and annual. Periodical cicadas, such as those in Broods XIII and XIX, emerge in large numbers after spending 13 or 17 years underground. These cicadas have distinctive red eyes and wing veins. Annual cicadas, in contrast, emerge yearly in smaller numbers and are predominantly green.
The periodical cicadas belong to the genus Magicicada, which includes several species grouped into Decim, Cassini, and Decula. These groups consist of both 13-year and 17-year cycle broods.
The Lifecycle and Emergence of Cicadas
Cicadas have an almost mythical ability to count time, spending 13 to 17 years underground as nymphs feeding on tree root xylem. They emerge when the soil temperature reaches about 64.4°F. Interestingly, even laboratory-reared nymphs, kept for the final nine months of their growth period, emerge synchronously, suggesting an innate timing mechanism.
Are Cicadas Harmful?
Cicadas pose no direct threat to humans or pets, and are not harmful unless consumed in large quantities by those with shellfish allergies. While they feed on tree roots and later, potentially, on above-ground parts of trees, their overall impact on tree health is negligible. In fact, their lifecycle contributes positively to the ecosystem by enhancing soil fertility through the decomposition of their bodies, which benefits soil bacteria and fungi.
The Unique Sound of Cicadas
Male cicadas are responsible for the characteristic loud noise, which is among the loudest produced by any insect. This sound is created not by leg rubbing, as in some other insects, but by rapidly vibrating specialized structures called tymbals on their abdomens.
While cicadas may be loud and appear in overwhelming numbers, their emergence is a natural spectacle that contributes positively to the ecological balance. They might be noisy, but they play a critical role in their ecosystem, showcasing the marvels of nature’s cycles.