Mayflies are called 'one day flies' in many languages, for example 'Dagslända' in Swedish. Depending on the species, the lifespan of an adult is from a few hours to a few days. You often find them by the lake in the evening, flying up and down, like elves doing their last dance. After all, one day is a lifetime. Södermanland, Sweden. Posted on September 2 2014.