【明報專訊】Billions of periodical cicadas (周期蟬) are coming out from the ground in the American East and Midwest. They belong to Brood X, the largest of their kinds. Appearing every 17 years, they're ravaging US regions including but not limited to Washington, DC. Up to 1.5 million of the insects can come out of the ground per acre of land, translating into tens of billions in total. Unlike locusts, which destroy crops, cicadas come out only for a few weeks to feed on trees, and also, as adults, to mate. Though looking a bit gross, they're actually edible and have a lot of protein! The magic number ''17'' is still now clouded in mystery but some experts reckon it to be a regular period of time to escape from their predators. ̷̷ Text: Staff Reporter ̷