Cicadas overwhelm tree branches across the Mid-Atlantic once every 17 years, like clockwork. But something — some suspect it’s climate change — could be sounding their alarm clocks four years early.
In recent days, the red-eyed, nugget-shaped insects have been spotted crawling out from beneath trees from Northern Virginia to Bel Air, Md., in large — though not overwhelming — numbers. The phenomenon is confusing entomologists, who weren’t expecting to see many of the screeching insects in the region until 2021.
Small numbers of cicadas can sometimes grow fast enough to emerge four years early. But there were 1,000 reports of cicadas up and down the Interstate 95 corridor on just two recent days, more than scientists expected.
Cicada lovers are wondering whether the numerous reports are simply a sign of how easy the Internet has made it to track the periodic rite of spring — or whether climate change is nudging more cicadas to venture aboveground early.
Scientists are asking residents to help them figure it out, using online reporting tools that didn’t exist during earlier cicada cycles. They’re collecting reports of cicada activity, which could continue for the next month, and also memories of how those conditions compare to past cicada seasons.
The data could help scientists investigate what is, for now, just a hypothesis: that longer growing seasons linked to climate change may have shortened the life cycle of many 17-year cicadas and could end up creating new cycles of timekeeping broods.
“You could see many more individuals coming out four years early, and eventually those could become so numerous that they’re self-reproducing,” said Chris Simon, a professor of ecology and evolutionary biology at the University of Connecticut.
Cicada swarms are impossible to miss when they arrive in earnest every 17 years, numbering in the billions or trillions, according to Mike Raupp, an entomologist at the University of Maryland at College Park.
A group known as Brood X last covered tree branches — and eventually sidewalks — across Maryland in 2004. A separate class, Brood VI, is now blanketing parts of the Carolinas and Georgia.
Cicadas spend nearly all of their lives underground, feeding on tree roots. Scientists suggest they have some sort of biological clock that counts the trees’ annual cycles of growth and hibernation. Once it hits 13 or 17 years, they emerge to reproduce, then die within about a month.
It is thought the cycles give the cicadas a biological advantage, rarely lining up with cyclical peaks in the numbers of their predators.
But scientists say there are always small subsets of the 17-year cicada broods that don’t wait the full cycle before emerging. These experts think cicadas “count” in fours, and if they are big enough after 13 years, some crawl out sooner.
It’s possible that climate change is helping more of them grow faster, Simon said.
“If the conditions are really good, then a lot of them will come out,” she said. “The longer the growing season, the higher the chance that a very large number will be ready four years early.”
Entomologists began crowdsourcing cicada sightings from across the country about a decade ago at Magicicada.org — a site whose name references periodical cicadas’ biological genus. The reports provide richly detailed data points mapping the density and breadth of 15 distinct cicada broods across the eastern United States.
But this is the first chance they have to so closely monitor Brood X. The last time any members of that brood emerged early was in 2000, so data is more anecdotal and localized.
It’s still early in the season to get a good gauge of the insects’ numbers. They don’t emerge until soil reaches 64 degrees, so entomologists expect more to come out as temperatures surge into the 80s and 90s.