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Although some cicadas make an appearance every year, the emergence of periodical cicada broods is always a memorable event. Billions of insects briefly surface to mate after spending years underground. North America is home to 15 periodical cicada broods (12 broods of 17-year cicadas and three broods of 13-year cicadas), so it makes sense that sometimes their aboveground appearances overlap. That’s exactly what will happen this spring in an event that could bring an estimated one trillion cicadas to the surface, covering 16 U.S. states in the Midwest and Southeast.
The overlap of Brood XIII (the Northern Illinois Brood, which emerges every 17 years) and Brood XIX (the Great Southern Brood, which emerges every 13 years) only happens once every 221 years. The last time these cycles synchronized was in 1803, and the next time will be in 2245. So if you’d like to see more cicadas than you could ever possibly count, this is the year to do it.
Only a small geographic overlap of the two broods is expected to occur, most likely in central Illinois. Brood XIII has also historically emerged in Iowa, Wisconsin, and Indiana. Brood XIX has been much more widespread, covering parts of Missouri, Arkansas, Louisiana, Mississippi, Alabama, Kentucky, Tennessee, Georgia, South Carolina, North Carolina, Virginia, and Maryland.
Reactions to cicadas tend to be mixed, and some residents in the emergence zones will undoubtedly attempt to leave home and avoid the insects altogether. Others, especially entomologists and curious nature fans, will no doubt be intrigued by this rare event. The overlapping region will be especially interesting, with scientists wondering whether the two broods will interbreed and possibly create a new cicada lineage. Interested in helping scientists learn more about the cicadas’ range? You can report your own sightings using the Cicada Safari app, which has received over 500,000 photos and videos since cicada expert and biology professor Gene Kritsky launched it in 2019.
If you’re not usually enamored of bugs, consider this: cicadas are beneficial to the ecosystems where they emerge. Their tunnels help aerate soil, while their exoskeletons and bodies offer nutrients to plants and food to predators like birds and small mammals. They spend much of their time in trees, where the females lay their eggs. Humans have nothing to fear from cicadas (which are actually edible), however unsettling it may feel to hear the "crunch" of accidentally stepping on a cicada exoskeleton or carcass. Cicadas do not carry diseases, nor do they sting or bite. The most annoying thing about them is their mating “song,” which sounds like a high-pitched buzz when countless insects simultaneously join in.
When periodical cicadas emerge from the ground, they are still nymphs. Becoming mature involves shedding their exoskeleton, taking flight, and hardening their skin. They will then begin their mating calls so that they can lay eggs. The whole event lasts around six weeks, culminating in the death of the adult cicadas. The cycle begins again when a new generation of cicada nymphs hatches from the eggs and tunnels underground, where they will spend the next 13 or 17 years eating tree roots.
Cicadaphile or cicadaphobe?
- The emergence of cicadas usually begins when soil temperatures reach 64 degrees Fahrenheit (17.8 degrees Celsius). Depending on the location, this will occur sometime between late April and June. The entire emergence should be over by early July.
- The New York Times calculated that if you lined up one trillion cicadas end to end, they would cover a distance of 15,782,828 miles (25,400,00 km). That’s roughly equal to 33 times the distance between Earth and the Moon.
- The raucous mating calls of male cicadas can reach close to 100 decibels, a sound intensity similar to that of a chainsaw.