Everything you wanted to know about 17-year periodical cicadas.

If Cicadas Only Come Around Every 17 Years, Why Do I Hear About Them All the Time?

If Cicadas Only Come Around Every 17 Years, Why Do I Hear About Them All the Time?

The state of the universe.
May 23 2016 7:31 AM

What Is Up With Cicadas?

Why they come out so infrequently, what they do in the interim, and most importantly—are they edible?

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Cicadas are the longest-lived insects on Earth.

Brent Miles/iStock

Why are we here?

Because cicadas are coming. 

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Cicadas?

I’d say it’s a little bit better than winter in Westeros, but not much. Alien-looking and demon-eyed, these inch-and-a-half-long insects spend the majority of their lives underground and out of sight, feasting on the juices of tree roots. This summer, after 17 years of subterranean dwelling, millions of them will burst into the above-ground world in a blaze of glory in many parts of the United States. They will shed their adolescent skins, let their new soft white outsides harden into a brown exoskeleton, and launch themselves upon the skies, a short-lived epidemic upon the Earth.

So they only emerge every 17 years?

Well, sort of. I’m talking about periodical cicadas, and those guys only appear every 17 years or every 13 years. (There is another species of cicada, the annual cicada, that emerge every 2-5 years.) Periodical cicadas are the longest-lived insects on Earth.* They’re essentially time-travelers: After reaching their full size underground, they can remain for years in a state of suspended development—like Austin Powers freezing himself for 30 years or Han Solo frozen in carbonite—while the rest of their brood mates catch up. Plus, if conditions aren’t ideal, they can emerge either four years early or four years late, creating new broods and even species. (If only we could cocoon ourselves underground for four years to wait out a potential Donald Trump presidency!)

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Then why does it feel like I hear about them all the damn time?

Because you do. Different broods are staggered over time and scattered across the United States. That means that while a particular brood may only emerge in the upper East Coast once every 17 (or 13) years, a brood is almost certainly emerging somewhere during most of those off years. Most likely, you’re hearing about different broods every year.

So if a brood emerges somewhere every year, then what’s so special about this year?

An excellent question. This year we are seeing the emergence of Brood V, which has been sleeping since 1999. Brood V happens to be spread out across many populous areas of the United States, including Ohio, Pennsylvania, Virginia, West Virginia, Maryland and Long Island, New York. (Due to an especially cool spring, we expect to see them around May 23.) But honestly, it’s a medium-size brood. Much of the to-do is just media hype.

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How should I feel about this oncoming insect invasion if I live in one of the affected areas?

Enthralled! You should count yourself lucky to occupy both the location and date of this once-every-17-years occurrence. A rare, spectacular, and cyclical phenomenon unique to North America—periodical cicadas do exist in Fiji and northeast India, but they are not as long-lived—cicadas are basically a midlatitude version of the Northern Lights. At least, to insect researchers: “This beats monarchs,” says Chris Simon, an ecologist and evolutionary biologist at the University of Connecticut. People who profess to hate cicadas, she says, are “people in general who hate nature.”

To find out if you will ever get to experience such an event, please see our cicada tracker:

Can I eat them?

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Dude, what is your problem? Ask me something else.

Why are there so many of them?

It’s all about evolutionary strategy. Your mother invested heavily in you: She nursed you, fed you, maybe even paid for your schooling. As a result, you are relatively likely to survive and thrive. Cicada moms employ a different strategy. Like fish that spew out great clouds of spawn, each female cicada lays up to 600 eggs, depositing them into slits she cuts in the twigs and branches of trees before taking off and basically hoping for the best. Those eggs soon hatch larvae that rain down upon the earth and burrow underground to fend for themselves. Naturally, up to 98 percent die, because life for cicadas is a cruel and merciless crapshoot.

OK, but there are still a ton of adult cicadas.

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You’re right. Adult cicadas engage in a self-sacrificing strategy called predator satiation: By emerging in droves, they hope to glut most of their predators, so that the cicada survivors can enjoy a window of predator-free mating time. And boy, do cicadas have a lot of predators: squirrels, waterfowl, wasps, ducks, cats, dogs, birds, snakes, turtles, spiders, fish. I mean, they’re basically packets of fat that have been plumping themselves in the shade for years. “It’s a great year to be an ant, or a bird, or anything,” says John Cooley, an ecologist and evolutionary biologist who works with Simon and also runs the site magicicada.org.

Why 13 or 17 years?

Mathematicians have theorized that cicada life spans tend to fall in prime numbers because it makes it harder for short-lived predators to match up their life spans with their emergence. But their elongated life spans may simply be random, and the numbers 13 and 17 a coincidence, says Simon. She should know: She’s been studying cicadas for more than 40 years, which is almost three broods! 

I can’t even wake up when I set an alarm. How do these bugs know when to come out?

Welcome to the reason this genus is known as Magicicada. (Yes, really.) We know how cicadas detect seasons: They get important clues about where trees are in the growth cycle from the composition of the roots they feed on. But no one knows for sure how they keep track of how many years have passed. It’s likely that the gene or genes responsible are the same ones involved in timing in other organisms—such as the ones that tell birds how and when to fly south for the winter and salmon how to swim to their ancestral breeding pond. “We know it’s some sort of molecular clock,” says Simon. But researchers will have to study those kinds of timing genes in depth before they unravel this mystery.

Wow, cicadas certainly do sound magical. But how do they taste?

Are we seriously doing this? Fine. It’s true that some Native Americans have historically eaten cicadas, considering them a gift during times of famine, says Cooley. This is confirmed in a 1907 booklet on periodical cicadas published by the U.S. Department of Agriculture: “The Indians [sic] make the different species of Cicada an article of diet, every year gathering quantities of them and preparing them for the table by roasting in a hot oven, stirring until they are well browned.” (One USDA employee stated his preference for them battered and fried, like shrimp, but really does not recommend them in stew, where they disintegrate into “bits of flabby skin.”) Animals eat them “greedily and with impunity,” according to a doctor quoted in the booklet.

Should I eat them?

I mean, theoretically, go for it. Cicadas are a pretty wholesome, organic food, having lived on pure tree roots for their entire lives. However, if you do plan on eating cicadas, keep in mind: Studies have suggested that they accumulate the toxin mercury in their bodies, and experts have expressed concern for eating them in places that have been treated with pesticides and herbicides, which they have had ample time to absorb. Finally, you’ll want to capture them either when they first emerge or when they’ve just molted and are still soft, rather than after they harden and darken into virtual inedibility.

What should I expect if I eat a cicada?

Adult male cicadas are “more crunch than munch,” according to a National Geographic article on best practices for cicada eating. “The plant-based diet gives them a green, asparagus-like flavor, especially when eaten raw or boiled.” The USDA booklet also observed that cicadas were full of “a thick white matter like cream,” attracting rooting hogs and making them basically the eclairs of the insect world. I asked Cooley about what this mysterious white substance could be. “It’s basically fat,” he said, adding that it can be difficult to prepare cicadas as museum specimens because they’re such fat, juicy grease balls. They’re so oily, people have even used them for soap-making. Yum!

Happy cicadapocalypse!

*Update, May 23, 2016: This paragraph has been updated to clarify the difference between periodical cicadas and annual cicadas. (Return.)
 

Rachel E. Gross is the science web editor at Smithsonian.