Ephemeroptera - The Mayflies

Mayflies are among the most ancient of insects, evolving in the Carboniferous period some 350-280 million years ago. The ordinal name Ephemeroptera is derived from the Greek word "ephemeros", which means "lasting a day". As many people know, adult mayflies live only a few days at most. However, this brief stage occurs after the mayfly has spent much time as an aquatic larva - as long as 3 years in some species. It has been said that this adult, sexual form is merely a vehicle which the larvae use to create more larvae! Mayflies are predominantly associated with freshwater but a few have adapted to live in brackish water; one species has terrestrial larvae. Adults emerge solely to mate and die. They do not eat, filling their guts with air instead, adding to their delicate nature. Unique among insects, mayflies first pass through a temporary phase called a "subimago", a non-sexual adult. Lacking the colors of the true adult into which it will soon molt, this is the smoky-winged “dun” used by fly fishermen. In fact, mayflies constitute the primary basis for both the sport and the technique of fly fishing, not to mention fly tying. In English vernacular, mayflies are known by many other names; willowflies, shadflies, drakes, and spinners, to name but a few. In the temperate parts of Earth they emerge in summer but in the tropics, they may emerge year round. This wide range of species (about 2,500 known so far) feeds on everything from algae to other invertebrates. Some are filter feeders, using long setae on specially adapted forelegs and mouthparts to collect floating food particles. Many mayfly larvae are highly sensitive to toxins in their water supply, particularly those from acid rain. As such, they are excellent indicators of a stream’s health. Mayflies have been exterminated from many bodies of water in both the U.S.A. and Europe, to the loss of much potential fish stock. This is a sad story for an insect so vital to the quality of freshwater ecosystems. Fly fisherman, unite!

97_15_thumb.jpgBurrowing Mayfly (Hexagenia sp.)