Cicadas are coming: Everything you need to know about Brood X, the biggest emergence in 17 years Updated May 07, 11:08 AM; Posted May 07, 11:08 AM 28 Facebook Share By Christine Condon, The Baltimore Sun (TNS) They’re coming. The biggest cicada emergence in the Eastern U.S. since 2004 is imminent. Here’s what you need to know about Brood X: What is a cicada? Although oft-compared to the Biblical plague, periodical cicadas are not locusts. (If you’re wondering, locusts are a type of grasshopper.) The large, winged bugs with beady red eyes grow underground by sucking on tree roots for either 13 or 17 years, before emerging in spectacular numbers to mate and lay eggs in the treetops.