And then another. And another. And four more. In maybe a third of a square foot of dirt, the University of Maryland entomologists find at least seven cicadas — a rate just shy of a million per acre. A nearby yard yielded a rate closer to 1.5 million. And there’s much more afoot. Trillions of the red-eyed black bugs are coming, scientists say. Within days, a couple weeks at most, the cicadas of Brood X (the X is the Roman numeral for 10) will emerge after 17 years underground. There are many broods of periodic cicadas that appear on rigid schedules in different years, but this is one of the largest and most noticeable. They’ll be in 15 statesfrom Indiana to Georgia to New York; they’re coming out now in mass numbers in Tennessee and North Carolina.