Nature at its craziest with trillions of cicadas

City talk | Seth Borenstein 14 May 2021

Sifting through a shovel load of earth in a garden, University of Maryland entomologists Michael Raupp and Paula Shrewsbury find a cicada nymph, then six more. And trillions more of the red-eyed, black bugs are coming.

Within days the cicadas of Brood X will emerge after 17 years underground. There are many broods of cicadas that appear on rigid schedules in different years, but this is one of the largest and most noticeable. They'll be in 15 US states from Indiana to Georgia to New York.

When all the broods have emerged gardens can look like undulating waves, and the bug chorus is lawnmower loud.

The cicadas will mostly come out at dusk to avoid predators. They'll try to climb trees or anything vertical to shed their skins and survive.

It's one of nature's weirdest events, featuring sex, a race against death, evolution and what can sound like a bad science fiction movie soundtrack.

Some people are repulsed. But scientists say the arrival of Brood X is a sign that despite pollution, climate change and biodiversity loss something is still right with nature.

Raupp presents the narrative of a cicada lifespan with the verve of a Hollywood blockbuster: "You've got a creature that spends 17 years isolated underground sucking on plant sap. In the 17th year these teenagers are going to come up by the billions and trillions. They're going to try to best everything on the planet that wants to eat them when they're trying to grow up. They're just trying to be adults, shed that skin, get wings, go to the treetops.

"Once in the treetops it's all going to be about romance. It's only the males that sing. It's going to be a big boy band up there as the males try to woo a female to be the mother of his nymphs. If she likes his songs she's going to click her wings. They're going to have some wild sex in the treetop.

"Then she's going to move out to the small branches, lay eggs, and it's all going to be over in weeks. They're going to tumble down to basically fertilize the plants from which they were spawned. Six weeks later the tiny nymphs are going to tumble from the treetops, bounce twice, burrow down into the soil, go underground for 17 years.

"This is one of the craziest life cycles of any creature on the planet."

America is the only place in the world that has periodic cicadas that stay underground for either 13 or 17 years, says entomologist John Cooley of the University of Connecticut.

The bugs only emerge in large numbers when the ground temperature is at 64 degrees F. That's happening earlier in recent years with climate change. Before 1950 they emerged at the end of May.

Cicadas that come out early are soon eaten by predators. So they evolved a key survival technique: overwhelming numbers. There are too many to be all eaten when they emerge at once, so some will survive and reproduce.

This is not an invasion. The cicadas have been here the entire time, quietly feeding off tree roots underground. Not asleep, just moving slowly and waiting for their body clocks to tell them it's time to go up and breed. They've been in America for millions of years.

When they emerge it gets noisy - 105 decibels noisy, like "a singles bar gone horribly, horribly wrong," Cooley says. There are three distinct cicada species and each has its own mating song.

The only plants they can damage are young trees, but they can be netted. The year after a big batch of cicadas all trees do better as dead bugs are fertilizer.

Some people dread the cicada emergence, perhaps because when cicadas die in mass numbers they smell bad.

But for scientists like Cooley there's beauty in their life cycle.

"This is a feel-good story," he says. "When they come out it's a great sign forests are in good shape. All is as it is supposed to be."

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