Adults often emerge from the stream simultaneously in an event called an emergence or hatch. Strongly attracted to light, mayflies have been known to completely cover the fronts of cars parked next to bridges or to nearly smother campfires. The adult stage lasts from a few hours to several days and is devoted to reproductive behavior. Unique among aquatic insects, mayflies have a fully winged terrestrial stage, a subimago , before their sexually mature adult stage. The subimago is dull in appearance in contrast to the clear-winged adult.
Most species complete their life cycle within one year.
Their nymphs, many of which prefer slow-moving or still water, are commonly found in lakes, ponds, streams and marshes and can be sensitive to habitat degradation. About 415 species are found in North America. The name Odonata comes from odon , meaning teeth. The labium is shaped like a long arm with hooks at the tips and is folded beneath the nymph's head. When prey pass, the labium shoots out in a split second to seize the creature.