The larvae of mayflies (order Ephemeroptera) live in rivers and lakes where they grow and molt until the adults emerge, mate and lay eggs before they die after a very short life. The emergence of the adults occurs synchronously, and often around full moon as shown here for the African mayfly Povilla adusta (picture modified from Corbet et al., 1974, J. Zool.). Drawing to the last larval instar: Mareike Förster. Large picture on the right: mayflies hatch on the St. Louis River in Jay Cooke State Park, Minnesota (taken by Brian Hoffman on July 19, 2018). Small picture on the bottom left: freshly emerged mayfly resting on gras near to the River Wey (taken by Johan J. Ingles-Le Nobel on May 26, 2016). Small picture on the bottom middle: mayflies on a car left under a streetlight over the night (taken by Brian Rutledge on June 22, 2005).