We Paved Cicada Paradise
Seventeen years is a long time in the development cycle of a city. In 17 years, neighborhoods turn over, highways grow wider, and new high-rises nudge from conception to construction to capacity. In 17 years, whole housing markets boom and bust as built-from-scratch communities curl out farther into the countryside. In 17 years, a forest easily becomes a subdivision, a meadow a new mall.
Now imagine you're a cicada.
What happens to nature's most mysterious periodicals when we pave over them? If a magicicada burrows underground to spend the next 17 years in waiting, and we then drop a couple of colonials on top, can the little guy even get out again?
As it turns out, probably not.
"They have a tight connection with the tree," says Dan Babbitt, the manager of the insect zoo at the Smithsonian's National Museum of Natural History. Cicadas spend their underground years feeding off the roots of trees. Then when they're ready to come up, they crawl back out along the tree trunk to the branches where they lay their eggs, all in the hopes that the next generation of cicadas will fall back into the soil, burrow down to the roots, and feed there for another 17 years.
This is why leafy residential neighborhoods often have some of the best cicada sightings (and sounds). It's also why the absolute worst thing we could do to the creatures is clear-cut whole stretches of once-rural land for new development while they're down there. Get rid of the trees, and you get rid of the cicadas. And re-planting those sad saplings common along many freshly paved roads in the exurbs won't help.
"Digging out an area the size of a city block or a house to do construction is not going to affect them too greatly," Babbitt says. Cicadas, after all, are a species whose survival is built on numbers. "But if that’s happening all over, obviously, then yes."
And no, he adds, you cannot plow up a patch of land containing cicadas, dump it elsewhere, and expect them to emerge from there.
This year's Brood II cicadas are currently appearing on the East Coast (although not quite with the drama we initially expected). But John Cooley, a cicada researcher in Connecticut, has seen evidence of extinction elsewhere, in the sprawling subdivisions around Champaign-Urbana in Central Illinois.
"When they go out and build these things around Champaign-Urbana, they cut the trees down, they bring in the bulldozers, they pull up the top soil, and they stick the houses down," Cooley says. "None of the cicadas in the ground there would have survived that. None of anything in the ground would have survived that."
Some periodical cicadas do well in older, tree-lined suburbs, Cooley says, those places where houses were built slowly over time, "where they didn't take the big trees." Across history, it's hard to tell if the shape and geography of broods has altered significantly around the footprint of expanding cities. Early records on when and where they appeared – and which broods were which – aren't all that reliable. Some "straggler" cicadas also appear off the cycle of the rest of a brood, further confusing history's witnesses.
The problem, Cooley says, is "when its wholesale and all at once. It's the pace and scale of the development that can lead to extinction."
Cooley has mapped a few broods whose ranges have noticeably contracted with time. Brood VII in upstate New York once emerged around the Finger Lakes region but now appears primarily south of Syracuse. And Brood XI in Connecticut hasn't been seen since 1954. But these patterns may have more to do with climate than deforestation.
We do know, though, that once cicadas disappear form an area, they'd likely have a rough time returning, even if the habitat improved. In that long life cycle tied to the roots and branches of an individual tree, cicadas seldom migrate very far.
The last known location of Brood XI, northeast of Hartford, Conn., today has a healthy and interconnected forest of oaks and hickory. During his research, Cooley stumbled across a photo of the same area taken more than century ago.
"You look at the photograph in 1900, and it’s not very good habitat: There's little scraggly woods connected by fence rows," Cooley says. Today, things actually look much better. "But the cicadas aren’t there," he says. "That just reinforces the idea that they have a very difficult time building their population up once they're down."