Billions of winged bugs rising within the U.S.

Ready or not, the cicadas are back.

In the eastern United States and parts of the Midwest, billions of cicadas emerge from underground for the first time in 17 years to partake in a noisy, month-long mating ritual.

Cicada sightings have been reported in several states, including Virginia, Maryland, and Georgia. However, with warm temperatures expected for much of the east coast over the next few days, large numbers of the winged insects could be outside this week.

“It’s a unique experience because you can really take it for a month or so,” said John Cooley, an entomologist at the University of Connecticut. “There may be trillions of ants, but most of the time they are ignored. They are big, loud, funny-looking, charismatic, active insects, and they really can’t be ignored.”

The cicadas now appearing are periodic insects. They spend most of their lives underground feeding on tree roots before tunneling to the surface in search of mates.

Six species of cicada are native to the eastern United States. This year, three species of insects emerge that live in 17-year cycles – a group called Brood X.

The cicadas usually emerge from underground once the ground reaches a temperature of about 64 degrees Fahrenheit, Cooley said.

“They count the seasonal cycles to get the correct year and then wait for an evening that isn’t stormy or rainy when the ground temperature is just right and then they come out,” he said.

As soon as the insects have buried themselves on the surface, they shed their nymph exoskeletons and unfold their wings. It then takes several days for their adults’ skin to harden.

Then the frenzy begins.

Just weeks to find a partner and lay their eggs before dying, the cicadas are in a race against time. The insects send out a loud, high-pitched pairing song that can reach up to 100 decibels, which is roughly the equivalent of a motorcycle or jackhammer, Cooley said.

But while the cicadas sound and look ominous – especially with their blood-red eyes – they are not harmful to humans. The same applies to pets, which can feed on the discarded cicada exoskeletons.

“They’re not poisonous, but you don’t want your dog to eat them,” Cooley said.

Researchers like Cooley want to study Brood X cicadas in this narrow window when they are active above ground. Scientists, for example, are interested in mapping their reach and behavioral changes between cycles.

“There were a lot of cicadas that went wrong and came out four years early in 2017,” Cooley said. “We’ve pinpointed these locations and want to see how many cicadas come out this time. Maybe they were areas with an unusual abundance of cicadas, or maybe something strange was going on.”

And while the appearance of billions – even trillions – of noisy winged insects may fill some people with fear and anxiety, Cooley hopes people will enjoy and appreciate the experience.

“This is such an interesting and rare phenomenon,” he said. “Enjoy it while it’s out and remember it won’t happen for the next 17 years.”

Denise Chow is a reporter for NBC News Science focusing on general science and climate change.