Mayflies are aquatic insects belonging to the order Ephemeroptera. This order is part of an . Adult mayflies, or imagos, are relatively primitive in structure, exhibiting traits that were probably present in the first flying insects. These include long.
Adult mayflies of North American species range in body length, exclusive of tails, from 2.5 mm (0.1 inch) for Caenis to 32 mm (more than an inch) for Hexagenia.
Adult mayflies are fundamental to the sport of fly fishing. In North America alone, over 150 species of mayflies have served as "models" for creating imitative fly.