A bug’s life: Cicada emergence is a mysterious, massive phenomenon

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A 17-year cicada. File photo. A 17-year cicada. File photo.

Sachin Gadani and a few friends recently spent a weekend combing Charlottesville for cicadas.

The UVA MD-PhD graduate student is head of the University’s entomology club, and he and several fellow amateur bug lovers haven’t had to look hard to find the first local representatives of one of the greatest spectacles of the insect world: the spring emergence of a massive brood of 17-year cicadas.

The big, orange-and-black bugs’ presence here is spotty, Gadani said, but “there are certain areas that are just teeming with them right now. My friend said he can’t even walk out of his house because there are so many cicadas smacking him in the face.”

Magicicada septendecim is one of several species in the eastern U.S. that spends nearly two decades underground before crawling from the soil and taking to the trees to sing, mate, lay eggs, and die—all in the course of a few months.

In “good locations” in Virginia, said Eric Day, the entomologist in charge of Virginia Tech’s Insect Identification Lab, their numbers could reach 1 million per acre.

“The word ‘invasion’ gets used a lot,” he said. And that leads to comparisons to the unwelcome hordes of invasive brown marmorated stink bugs and Asian lady beetles that regularly swarm local homes, their numbers unchecked by natural predators.

But that’s not quite fair, said Day, considering the cicada is no invader.

“You’re kind of throwing them in with a bad lot there,” he said. “These things are native, and for the most part, they’re not really causing that much damage.”

Indeed, while they might look like a plague of locusts, the large, winged insects won’t be ravaging any crops. Nor do they bite or sting. What they will do is lay a lot of eggs at the ends of deciduous tree branches, Day explained—enough that many branch tips will snap off. That’s a concern for orchard owners, who could see the twigs of young fruit trees wrecked as they’re turned into cicada nurseries.

“A tree may take a long time to recover from that kind of damage,” he said, but the reliable cycle of broods means people have plenty of time to plan, and most fruit growers know not to plant new trees for a year or two before a major emergence like this one.

The bugs’ rigid regularity gives us a lot to wonder at. On the East Coast, there are 12 broods of 17-year cicadas, each on their own cycle—the longest of any insect species. Some years, none emerge, said Day, but Virginia is the stomping ground of two big populations: Brood X, which last hatched in 2004, and Brood II, which is just digging its way into the light now.

Researchers think the long wait between boom times and the fact that they come at prime-number intervals has helped the insects avoid syncing life cycles with animals that would feed on them exclusively. “That’s borne out in that there are virtually no specialized predators or parasites for periodic cicadas,” said Day.

But the reasons for the long period underground are still shrouded in mystery. “We have these theories, and the evidence seems to support them, but we don’t know,” he said.

The mystery may be part of why the big hatch-outs so thoroughly capture public attention. “It’s this cryptic, huge population of insects that people suddenly realize was here living under their yard in the tree roots, and then they come out of hiding,” said Day. And there’s something captivating about such a powerful reminder of the endless cycles of nature.

“I think people see them emerge, and it makes them think about what they were doing 17 years ago,” he said. “It’s a little bit of a trip for people.”

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