While they're here for a short time, they will be busy molting, mating and then will die off by the end of June. The influx of protein into ecosystems will fatten up other animals and spur reproduction. Brood X is one of 15 broods of periodical cicadas. Of the broods, Brood X is the largest range — with cicadas appearing throughout parts of the South, northeastern states and Midwest. It's also the brood that has the highest concentration which could send the numbers into the trillions. Where has Brood X emerged so far? According to uploads from the Ohio-based app Cicada Safari, Brood X has already began to emerge in Benton, Tennessee, a rural town 38 miles southwest of Chattanooga as well as parts of north Georgia. In photos that users snapped, all of the cicadas have black patches behind their eyes, said Gene Kritsky, a cicada expert and dean of the School of Behavioral and Natural Sciences at Mount St. Joseph University in Cincinnati.