For cicadas, it’s safety in numbers. Is climate change messing with your timing?

A cicada in sync with its brood is a cicada with a chance.

The synchronized emergence of insects is an evolutionary strategy, scientists say. Birds, raccoons, and other predators can only eat so much of them. Therefore, the more cicadas that emerge together, the greater the chances that more cicadas will survive to reproduce and pass on their genes.

“They have the strategy of safety in numbers,” said Chris Simon, a professor of ecology and evolutionary biology at the University of Connecticut who studies insects.

The rare cicadas that lose track of time and emerge without their relatives, on the other hand, are sometimes called “stragglers.” Most small groups of stragglers are snapped up and do not survive to reproduce.

“Natural selection has favored individuals that wait, because those that don’t wait are eaten,” Simon said.

This summer, the number of periodic cicadas is expected to be even higher, as two broods emerge at the same time. The last time these two appeared together was in 1803. Tens of billions of insects are predicted to come to the surface. Users of Cicada Safari appwhich was designed to report cicada sightings and help scientists track the insects, has recorded more than 1,000 sightings in Georgia and hundreds in North Carolina and Alabama.

Periodic cicadas fall into two brood categories, or age classes: those that take 13 years to emerge and those that take 17 years. The temperature appears to soar when they emerge, but how exactly they set their internal clocks or communicate when they must emerge from the ground together remains somewhat of a mystery.

Additionally, scientists say they have noticed some changes in the insects’ rhythms, which has led to hypotheses that rising temperatures may be altering the internal clocks of some periodic cicadas.

Gene Kritsky, an entomologist and cicada expert at Mount St. Joseph University in Ohio, said that as average temperatures have risen due to global warming, emergence dates have shifted earlier in the calendar year.

“Cicadas are climate bugs,” he said, adding, “They are now emerging almost 10 days to two weeks earlier than they did in 1940.”

John Cooley, a University of Connecticut cicada researcher who maps cicada broods, said he expects the insects’ distribution to shift north as the climate warms and the plant species they prefer move north.

He also noted an increase in reports of stragglers, a trend that intrigues researchers.

“If you look at the data, we definitely have more reports of mismatches now than in the past,” Cooley said. “That could be because there are more stragglers than in the past or because we have the internet and if you see this weird bug in your yard, you can send it in.”

Simon said Brood XIII, which is emerging this year, produced a record number of stragglers in 2020.

“This time four years ago, there were so many that they stayed out for four whole weeks,” she said. “They were not completely eaten. They were able to sing and lay eggs. Therefore, they could be forming a new population.”

“They are definitely responding to climate warming and the length of the growing season,” Simon added.

Simon has a theory about how climate change may be playing a role: She thinks rising temperatures are lengthening the growing seasons of the plants that cicadas feed on, speeding up the development of insects underground. This, in turn, can cause many more “laggards” to emerge early. Eventually, she said, the entire population will adapt and change the times.

Simon predicted that 17-year cicadas broods will moult to become 13-year cicadas. And 13-year cicadas can emerge every nine years.

If the theory proves true, it will be yet another example of how climate change is disrupting the regular rhythms that govern the natural world.

Periodical cicadas, which are harmless to people, are distributed throughout the Eastern and Midwestern United States. Unlike annual species of cicadas, which reappear every year, the emergence of cicadas like those now appearing in the Southeast is a special event. The US is home to 12 litters that emerge in 17-year cycles and three litters that have 13-year cycles.

During their years underground, periodic cicadas spend their time feeding on plant roots. Once above ground, they participate in a song-filled mating ritual, trying to lay eggs before they become lunch for a bird or a raccoon.

Scientists are still trying to figure out exactly how cicadas select a certain period of days to emerge together.

Although temperature clearly plays a role, soil temperatures are rarely uniform across cicadas’ habitat, and insects are often buried in different layers of soil. A study this year said there is no obvious explanation for the success of cicadas’ coordination and suggested that scientists investigate whether they can communicate underground.

“No one has ever studied this,” Simon said.

This article was originally published in NBCNews. with