By Catharin Shepard • Staff writer •

They’re loud, they’re alien-looking, and they’re coming soon to a tree near you – along with billions of their friends.

Singing cicadas are a hallmark of North Carolina’s warmer months. Louder than the croak of a spring peeper frog, more insistent than the buzz of a broken fluorescent light, the insects’ ear-piercing song makes passing the long, hot hours on a front porch an unforgettable experience.

Love them or hate them, there’s about to be a lot of them serenading the arrival of warm weather.

It’s been 17 years since a group of cicadas known as Brood X left their next generation to grow up underground. That brood is due to start tunneling to the surface to become adults over the next few weeks.

Brood X is the largest of the 17-year cicada broods, experts say. This year the cicadas are expected to be widespread in 15 states, ranging all the way from Michigan to Maryland to Georgia, and across North Carolina.

While there are always some species of “annual” cicadas around to liven up a summer day, the appearance of the insects known as “periodical cicadas” takes place in spring. Brood X – as in the Roman numeral for 10, not the letter “x” – is one of 21 “broods” of periodical cicadas, according to the North Carolina Cooperative Extension. The broods include several different species of periodical cicada that emerge on a set schedule like clockwork.

The insects spend either 13 or 17 years as flightless nymphs, eating tree roots underground. When the weather warms up, they emerge to molt and leave behind the empty skin that can often be found on tree trunks.

Once they’re molted, they survive about a month and during that time, focus entirely on finding a mate and laying eggs. The famous shrill song comes from male cicadas calling for a female mate, scientists with North Carolina State University say.

Although researchers counted and labeled 21 periodical cicada broods, some of them have gone extinct. Today there are 15 broods that still emerge in the eastern United States, according to the N.C. Cooperative Extension. Six of those periodical cicada broods emerge in some part of North Carolina.

This year it’s Brood X, last seen in 2004. The next big periodical cicada emergence will happen in 2024, and the following year will see a visit from Brood XIV. The biggest cicada brood in North Carolina is Brood II, which last emerged in 2013 and will emerge again in 2030.

When Brood X dies off, leaving their eggs to hatch and start a new cycle, their offspring won’t make their appearance until 2038.

Cicadas might look and sound alien, but they don’t have teeth and can’t bite. But they’re certainly loud: some can reach volumes of 100 decibels or more, similar to the noise level of a lawn mower or even a motorcycle.

People interested in learning more or helping out researchers as they track the brood’s emergence, can download the Cicada Safari app online at http://cicadasafari.org.