They’re coming — billions, perhaps trillions, of them within the next few weeks. They’re the Brood X cicadas that will emerge from below ground for the first time in 17 years.

As they crawl out via finger-size holes, they’ll mate and then make their way onto trees to lay eggs. After that, the adults will die and the nymphs that hatch from the eggs will fall out of the trees and burrow back into the ground — where they’ll stay holed up for another 17 years, until 2038, feeding on sap from tree roots.

Georgia is one of 15 states where Brood X cicadas will emerge, but their appearance — and loud buzzing — in the Peach State probably will be limited to parts of about 10 counties in North Georgia, including Union, White and Gilmer counties. They’re not expected to be seen or heard in great numbers in Atlanta.

Here’s the buzz on Brood X cicadas from University of Georgia entomologist Nancy Hinkle and some other experts.

— Brood X cicadas are types of periodical cicadas that emerge every 13-17 years in April and May. They have red eyes, black bodies and orange wings. On the other hand, annual cicadas (often called dog day cicadas) show up every year in Georgia during June through October. They have black eyes and green wings.

— After it begins, the emergence of the Brood X cicadas will last for about six weeks; then it will be over.

— Cicadas are harmless and don’t bite or sting. Despite their mind-boggling numbers, periodical cicadas don’t cause major ecological damage — and may be of some benefit such as soil enrichment.

— Periodical cicadas sing during the day; males call to attract mates. (Crickets, katydids and frogs sing at night.)

— Periodical cicadas occur only in the east; there are no populations west of the Mississippi.

— Just about all wildlife — including snakes — eat cicadas, finding them tasty, energy-packed morsels.

You can be of help to scientists studying cicadas. Go to Cicada Safari at cicadasafari.org to see how you can help.

IN THE SKY: From David Dundee, Tellus Science Museum astronomer: The moon will be full on Monday — the “Flower Moon,” as the Cherokee people called it. Mars is low in the southwest at dark and sets in the west a few hours later. Jupiter and Saturn rise in the east just after midnight.

Charles Seabrook can be reached at charles.seabrook@yahoo.com.