This weekend, two nature phenomena are colliding. The first is that April 30 marked the start of the City Nature Challenge (CNC), an international community science competition motivating people around the world to get outside and participate in science. The second is the emergence of Brood X cicadas, when billions of cicada nymphs arise from the soil and take to the trees across the East Coast and Midwest. The opportunity to track and observe Brood X only comes once every 17 years (13 for some other periodical broods) and the next brood to come to the DMV won’t emerge until 2025. Read more here .