Mayflies or shadflies are insects belonging to the order Ephemeroptera (from the Greek εφημερος, ephemeros = “short-lived” (literally “lasting a day” “daily” or “day-long”), πτερον, pteron = “wing”, referring to the brief lifespan 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 fresh water. The adults are short-lived, from a few minutes to a few days, depending on the species. About 2,500 species are known worldwide, including about 630 species in North America. [nggalbum id=3 template=extend]