Mayflies are insects which belong to the Order Ephemeroptera (from the Greek ephemeros = "short-lived", pteron = "wing", referring to the short life span of adults). They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies. They are aquatic insects whose immature stage (called naiad or, colloquially, nymph) usually lasts one year in freshwater.
