Mayflies

Mayflies have a simple metamorphosis, with three life-history stages: egg, nymph (or naiad), and adult. The nymphal stages are numerous and relatively protracted, generally lasting for at least one year. Mayfly nymphs occur in aquatic habitats, and account for most of the lifespan of mayflies. Some species have as many as 28 nymphal molts. The last, pre-adult stage occurs when a nymph rises to the water surface, molts, and develops into a winged form called a subimago, which flies a short distance, and usually rests on vegetation. Within a A mayfly. Photograph by Michael Lustbader/Photo Researchers, Inc. Reproduced by permission. day or so, the subimago molts into the terrestrial, sexually mature adult stage, which is generally found in close proximity to the aquatic nymphal habitat. Mayflies are the only insects that have an additional molt after they have developed functional wings.

Mayflies have soft, elongate bodies, with two or (most commonly) three, distinctive, thread-like appendages projecting from the end of their abdomen. Adult mayflies have short antennae and many-veined, roughly triangular, membranous wings. The wings are held erect and together over the body when the animal is at rest, and cannot be folded up as in most other orders of insects. The aquatic mayfly nymphs have distinctive, leaf-shaped appendages on the sides of their abdomen that serve as gills for the exchange of respiratory gases.

Larval mayflies are aquatic in fresh waters, and have mouthparts adapted for feeding on algae and other relatively soft, organic materials. Most mayflies are herbivores or detritivores, but a few species are carnivores of other aquatic invertebrates. Because they do not feed, adult mayflies have only vestigial mouthparts. Mayflies have large, compound eyes, and in many species the males are larger than the females, and have forelegs adapted for grasping the female during the nuptial (mating) flight. In most species the forewings are relatively large, while the hindwings may be absent, or are reduced in size compared with the forewings.

Adult mayflies do not feed and are short-lived, only living for a few hours or several days. This fact is reflected in the Latin root of the scientific name of this group of insects, Ephemeroptera, which refers to the highly ephemeral nature of the adult stage. The sole purpose of adult mayflies is procreation. To achieve this goal, adults of particular species emerge synchronously within a brief period of time. Adult mayflies sometimes occur in spectacularly large aggregations, in which the animals mate and deposit their eggs to water in frenzied swarms, and then die soon afterwards. Most of the mayflies in the swarm are males. The females fly briefly into the swarm, find a mate, and they couple then leave to copulate and lay their eggs.