Spring has sprung in the Northern Hemisphere, bringing with it a wide range of wildlife. Warming weather spurs lots of animals to get back to work after winter, including many familiar insects like bees, butterflies, crickets, and ladybugs.

And across eastern North America, spring also periodically brings another, even buzzier wildlife boom: huge swarms of "periodical cicadas," insects that spent 13 or 17 years living underground. This kind of cicada exists only in North America, with seven species divided into more than two dozen broods, each emerging in a different year.

This year, Brood IX cicadas are emerging in southwest Virginia, parts of North Carolina, and West Virginia after a 17-year hiatus. The group consists of three 17-year species (Magicicada septendecim, Magicicada cassini, and Magicicada septendecula), but not the green cicadas, which appear annually, according to Cicada Mania.

Normally, researchers will go out in force during the May-June window to see how this brood and others intersect, but this year, because of coronavirus, they are asking for citizen scientists to step in. To do that, you can download the Cicada Safari App — available for Android and Apple devices — and see where people are finding cicadas, and to report your own sightings.

What are cicadas?

Despite their ominous appearance and loud, overwhelming presence — affectionately dubbed "Cicadapocalypse" in recent years — cicadas are harmless to humans. Once they emerge, the herbivores are focused solely on finding mates and laying eggs. They carry no diseases, and they neither bite nor sting. And contrary to popular belief, they are not locusts (or even closely related to them).

Cicadas are large insects of the superfamily Cicadoidea. More than 3,390 species exist worldwide, according to Cicada Mania, inhabiting every continent but Antarctica. These are mostly annual species, also known as "summer cicadas," which emerge every year during the warm season. North America has summer cicadas, but they tend to emerge later in the year and have light green or brown bodies — a noticeable contrast to the black bodies, big red eyes and veiny translucent wings typical of periodical cicadas, which belong to the genus Magicicada.

When their year arrives, periodical cicadas typically emerge sometime in late spring. Andy Melton [CC BY-SA 2.0]/Flickr

Why do they wait so long?

The reason for these cicadas' long, impeccably timed life cycles still isn't well understood, but scientists think it may help buffer the insects against predators. Each brood's long subterranean hiatus forces would-be predators to find other sources of food, and when a brood finally does emerge, there are suddenly so many cicadas that predators are overwhelmed, an evolutionary strategy known as predator satiation.

But how do periodical cicadas know when it's finally time to party? "The year of cicada emergence is cued by what I and others believe to be an internal molecular clock," biologist Chris Simon told Entomology Today. "The clock is most likely calibrated by environmental cues that signify the passage of a year, such as the trees leafing out, changing the composition of the xylem fluid on which they feed."

Periodical cicadas emerge only briefly to mate, lay eggs and die. They spend the first 12 or 16 years of their lives (depending on the species) underground, sucking nutrients from tree roots and molting several times. Upon their final molt, they tunnel to the surface and males begin attracting females to mate. They do this by congregating and producing loud songs through membranes on their bodies. These songs — a sort of long, whirring buzz — can be as loud as 100 decibels. The cicadas then mate, females lay eggs and the process begins anew.

Brood awakening

Each brood of periodical cicadas covers a different swath of the U.S., although some broods overlap and "stragglers" sometimes emerge out of sync with their brood. In 2020, for example, some Brood X stragglers showed up in April, but the bulk of this brood isn't expected to appear until spring 2021 in Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, North Carolina, New Jersey, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and Washington D.C.

Cicadas emerge generally when the soil where they lie dormant reaches 64 degrees Fahrenheit (about 18 degrees Celsius). You can track the date the insects emerge in your area on Cicada Mania, use the app mentioned above, or ask longtime residents who likely remember the last time the swarms rose up. The season of periodical cicadas usually starts between April and June and should end by late July.

At their worst, periodical cicadas are irritating. They don't bite or sting, and they aren't toxic for humans to eat — the taste has been compared to everything from asparagus (reportedly an effect of their vegetarian diet) to lobster tail. Some places even celebrate the return of their local brood, as West Virginia University did with the 2016 Magicicada Festival, which marked the 21st-century debut of Brood V.

Still, cicadas' mating calls are famously loud, and they can dominate the soundtrack of outdoor areas during late spring and early summer. Once you've braced for the cicada onslaught, though, don't forget to take a moment to just sit back and enjoy the show. You won't get a chance to see or hear these bizarre visitors for another 17 years.