To the untrained eye, cicadas may look extremely similar to each other, characterized by their hard exoskeleton and distinctive drone.
But, as millions of residents of the southeastern and midwestern United States will soon discover in the spring of 2024, the different species of cicadas can vary widely in everything from their sound to their appearance to their behavior.
Two broods of cicadas — Broods XIX and XIII — are expected to emerge from the ground, culminating their life cycle by reproducing on the surface. There are also seven different species of periodical cicadas in eastern North America, four of which emerge every 13 years, and three of which emerge every 17 years. Most cicada broods include all of the species of cicadas on that life cycle.
That makes this year’s co-emergence unique — because Brood XIX is on a 13-year cycle and Brood XIII is on a 17-year cycle, we’ll be able to spot all seven different species of cicadas during the approximately one-month period that they’ll spend above ground.
Telling Cicada Species Apart
All seven species of periodical cicadas fall under the genus Magicicada. Yet while they share similar habits in their emergence patterns, John Cooley, a biologist at the University of Connecticut, says the differences between Magicicada species aren’t hard to spot.
“They all have very distinctive appearance and behavior,” he says.
Within the genus, there are three species groups — Decula, Cassini, and Decim. Each group contains at least one species that’s on a 13-year life cycle, and one that’s on a 17-year life c
Cicadas in different species groups often show key differences in their appearance and behavior, regardless of what life cycle they’re on. But species within the same species group are often extremely difficult to tell apart, even if they’re on different life cycles. According to research from Cooley’s team at UConn, “some species pairs can be distinguished only by life cycle and geographic distribution.”
For instance, M. neotredecim, a 13-year cicada species, and M. septendecim, a 17-year cicada species, will emerge geographically adjacent to each other in Illinois. But Cooley says that, because these are both Decim species, “you’re going to cross that line (between the two species’ ranges) and never know the difference.”
“Where the 13- and 17-year (cicadas) are in contact, there are no morphological, behavioral or known genetic differences between the two groups of species except life cycle,” he adds. “So it’s just going to look like the same cicadas, but they’re on a different cycle.”
Read More: The 2024 Cicada Emergence Is Coming, Here’s Everything to Know
Identifying Decim Cicadas
The Decim species group is the only one that contains three cicada species. M. tredecim and M. neotredecim are on 13-year life cycles and will emerge as part of Brood XIX, the “Great Southern Brood,” while M. septendecim cicadas are on 17-year cycles and will emerge this spring with Brood XIII in the midwest.
While all three Magicicada species groups have a common ancestor, experts say Decim cicadas differ the most from other cicadas. The Decim species group diverged from the ancestor of the Cassini and Decula groups some 3.9 million years ago, according to a 2013 study published in Biological Sciences.
Today, Decim cicadas are identifiable from others by the wide orange stripes on their abdomen, and the orange spot on their head.
Decim cicadas, including the m. septendecim species seen here, can be spotted by the wide orange stripes on their abdomen. (Credit: Jason Patrick Ross/Shutterstock)
Within the species group, Decim species have also evolved to have slightly different appearances and mating calls. Cicadas use their signature hum to communicate with each other, which is particularly important during their emergence to facilitate mating. The three species of Decim cicadas all have slightly different pitches in their mating calls, which Cooley’s team hypothesizes evolved to keep cicadas from trying to mate with those of a different species.
“You’ll be able to hear that difference quite well where (Decim cicadas) overlap,” Cooley says. “They don’t overlap across their entire range. It’s just a narrow band going down through Illinois and Missouri and into Arkansas. But where they do overlap, you will be able to hear the difference between the species.”
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Spotting Decula and Cassini Cicadas
The Decula species group contains the 13-year M. tredecula cicadas and the 17-year M. septendecula cicadas. They’re distinguished from other cicadas by narrow orange stripes on their abdomen.
Meanwhile, unlike the other species groups, Cassini cicadas don’t have any orange stripes on their abdomen. This species group contains M. tredecassini, which are on a 13-year cycle, and M. cassini, on a 17-year cycle.
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Listen Closely During the Emergence
All of these cicadas will also be visible during the spring 2024 co-emergence — M. tredecula and M. tredecassini will emerge with Brood XIX, while M. septendecula and M. cassini will emerge with Brood XIII.
Because both of these species groups each only contain one species on each life cycle, there’s been less research on the distinctive habits of Decula and Cassini species, whose ancestors began to evolve apart from each other about 2.5 million years ago. But like Decim cicadas, each of these species have a slightly different rhythm and pitch to their mating calls.
For those living in the range of this year’s cicada co-emergence, Cooley recommends keeping your eyes and ears open to spot the differences between the Magicicada species.
“There are probably a couple of thousand species of cicadas in the world, but fewer than ten do anything like this,” Cooley says. “This is one of those years where you can go see all seven of the species.”
Read More: The Cicada Emergence Is Likely Unavoidable, But There Are No Real Threats
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