The last time these broods co-emerged, the year was 1803, Thomas Jefferson was president, and the Louisiana Purchase had just been completed — which means many of the states where cicada love songs will soon fill the air were not even officially part of the nation yet.
As impressive as that is, this year’s entomological phenomenon will be extra-special for researchers hoping to unravel the evolutionary mysteries of bugs that only crawl out of the ground in roughly 13-year and 17-year intervals.
Broods are not the same thing as species, and each brood can contain multiple cicada species that can emerge in different places. In 2024, all seven cicada species will be represented, a coincidence that won’t happen again until 2037.
That means this year’s emergence will be a data-collecting gold mine.
One of the more unusual mysteries scientists hope to investigate involves a parasitic fungus that attacks adult cicadas, turning them into what one expert calls “flying saltshakers of death.”
“So it’s pretty spectacular, from the standpoint of a scientist that’s interested in cicadas,” said Matt Kasson, a mycologist at West Virginia University.
Cicadas are true bugs in the insect family Hemiptera. Famous for their repetitive courtship calls, cicada adults are large, loud and highly conspicuous. But most of a cicada’s life is spent below ground as a nymph.
Cicada nymphs are probably among the most underappreciated forest herbivores, since most of the time they’re out of sight, making a living by sucking juices out of the roots of trees and other plants. They emerge in the spring or summer, when the soil about a foot below ground reaches 64 degrees. Nymphs then climb up the nearest vertical object and molt into their adult form. Those winged adults spend their brief but riotous lives mating and, for the females, laying eggs.
Cicadas can be broken into two general types: annual cicadas, which tend to have black or green eyes and can be heard every year, and periodical cicadas, which usually have red eyes and only emerge in 13-year or 17-year intervals.
While they are nymphs, these long-lived insects must escape the cold by burrowing down below the frost line. In some parts of their range, such as Wisconsin, that can mean living at depths of more than five feet beneath the surface.
This makes every emergence important for scientists. If a researcher studying a species of zebra or puffin wants to take genetic samples, they may have to endure hostile environments or treacherous journeys, but at least those animals are almost guaranteed to be present in any given year. The same is not true for a given cicada species. They may technically be there, but they are too deep underground to find easily and to access without causing significant harm to the animals. (Kasson said he has tried, and he came up empty.)
In addition, cicada broods don’t usually sync up; it’s been nine years since such a thing last took place. And when they do overlap in time, they tend to be spread out in space, with emergences happening several states away from each other.
This means some questions can only be investigated in certain places at certain times, depending on which broods are on deck that year and which species they contain.
This year, though, cicadas from Brood XIX and Brood XIII will butt right up against each other, mostly in Illinois. And this is where things get scientifically exciting.
Kasson hopes to study a cicada-afflicting parasite known as Massospora. When this fascinating fungus infects an adult cicada, it floods the insect with amphetamine…
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