What Are Cicadas and How to Keep the Bugs Away Before Their 2021 Season Starts

After 17 years spent hibernating underground, vast swarms of cicadas collectively known as Brood 10 will emerge in more than a dozen U.S. states in the coming months. Here's what to expect.

Trillions of the insects, which are often mistakenly referred to as locusts, are actually what are known as "Periodical cicadas."

Unlike annual cicadas that crawl from the soil every year, multiple species that make up the vast colony will be seen this year for the first time since 2004, and are scheduled to take flight between May and late June.

The fully-grown cicadas are typically between 2-3 inches long with large clear wings and large eyes on each side of the head. Depending on the brood, the bugs will appear at either 13 or 17 year intervals.

Brood 10 cicadas include the Magicicada septendecim, the largest of the 17 year species recognisable by its thick orange stripes. Also included is Magicicada cassini and Magicicada septendecula, two species that are documented as having a black body with orange wings and legs.

The cicadas are known for "singing" during daylight, as males synchronize noises in an effort to attract females. The noises can hit 100 decibels and can reportedly be heard for up to half a mile in distance. While timing is loose, the locations are more predictable—as cicada groups surface in the same area as their parents first emerged.

Forecast for the spring of 2021, cicadas are set to emerge in Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, North Carolina, New Jersey, New York , Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and Washington, D.C., according to experts tracking them.

They will crawl out when the soil reaches 64 degrees fahrenheit, with the process sometimes being triggered by a spell of warmer rain.

Their lifespan is defined by a lengthy period spent living underground, followed by a brief blast of activity. When they reach adulthood, cicadas will live for up to four weeks. During that time, the males make noises to attract females, males and females mate, and the females lay fertilized eggs in plants and branches. From there, the hatched cicadas perish and the process starts again.

It is believed the species stays hidden for so long to evade predators, a process known as predator satiation. Essentially, it gives the cicadas a better chance at survival-by-numbers, emerging in such a vast swarm that predators eat some, but quickly become overwhelmed.

While some insects would be considered to be pests, these cicadas don't intentionally enter homes to find shelter, they won't bite humans and they don't chew on plant leaves—although they may attract killer wasps.

While the bugs won't munch on your favorite plant, they may still damage it while laying eggs. Cicadas don't have mouthparts that lets them chew or digest such vegetation. Instead, they drink sap, a fluid from trees rich in amino acids and minerals. They also don't transmit diseases.

Experts say there is little point using chemical treatments or insecticides in an attempt to protect your plants, mostly due to the cicadas' large numbers.

It is instead advised to remove them by hand, by lightly spraying a garden hose or by using netting to cover up any young or valuable plants.

In addition, people who don't want to risk plant or tree damage can wrap trunks or bushes with foil or tape to catch cicadas trying to feed or lay their eggs.

Michael J. Raupp, emeritus professor of entomology at the University of Maryland, previously told Newsweek the cicada event that will take place this year "is a wonderful opportunity for millions of people to witness and enjoy a remarkable biological phenomenon in their own backyard."

A cicada sits on a twig in a forest preserve June 11, 2007 in Willow Springs, Illinois. The cicada emerge from the ground and taken to the trees as part of a 17-year hatch cycle. Scott Olson/Getty Images