An adult cicada sheds its nymphal skin on the bark on an oak tree, Tuesday, May 4, 2021, on the University of Maryland campus in College Park, Md. Trillions of cicadas are about to emerge from 15 states in the U.S. East. Scientists say Brood X is one of the biggest for these bugs which come out only once every 17 years. (AP Photo/Carolyn Kaster)