Every year, a relatively small number of Magicicada cassinii, better known as the cicada insects emerge from the ground in the eastern United States. But once every 17 years, a truly massive brood of cicadas arrives in the mid-Atlantic and Midwest, filling the air with a deafening mating hum that can reach up to 100 decibels.
That phenomenon is named Brood X, or the Great Eastern Brood. It’s set to return in May 2021. For the five to six weeks that they’re above ground, the live cicadas — and their crunchy, discarded exoskeletons — will be impossible to miss. Here’s everything you need to know about this rare phenomenon…
What is Brood X?
Scientists group cicadas based on the year they emerge as adults after spending years developing underground. Brood X is the name for the big generation of cicadas due in the spring of 2021, just as in 2004 and 1987.
The coming Brood X (Brood 10 in Roman numerals) is the most widespread and prolific of the known generations. Through history, it has appeared as far west as Missouri, as far south as Georgia, as far north as Michigan and as far east as Long Island, New York.
Emerge once in 17 years
As it turns out, those long cycles are part of the cicada’s evolutionary strategy that dates back 1.8 million years, to the Pleistocene Epoch. Back then, summers could be unpredictably cold in the eastern United States. That’s a problem for cicadas: If the temperature lingers too long below 68 degrees, it gets too cold for them to mate and survive.
A brood can’t survive a cold summer above ground, but surviving a cold summer below ground is no problem.
In huge numbers
It’s not easy being a cicada. Once a cicada emerges above ground, it faces no shortage of predators. Birds, reptiles, fish, spiders, wasps and even household pets all see cicadas as protein-packed snacks. Many predators will completely change their behaviors during cicada years just to feed on them. To survive, cicadas need to show up in such massive numbers that their many, many predators just can’t eat them all.
How safe are plants and animals
Cicadas won’t hurt most plants. The bugs are, however, a danger to young trees, especially fruit trees. They won’t bite you unless they mistake you for a plant, they won’t decimate crops like locusts do, and they don’t spread disease. They’re not poisonous, either, so there’s no worry if your dog or cat eats one.
Largest of 15 known periodical cicada blooms in the US
• 17 years underground
• Feed on tree root sap
• Molt through five growth cycles
Life above ground: 4 – 6 weeks
• Shed exoskeleton
• Escape predators
• Lay eggs (females)
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