Common names are mays, mayfly, upwings, duns, dippers, spinners. Mayfly belongs to Ephemeroptera or Ephemeridae, suborder Schistonota & Pannota.

If there is one aquatic insect that is always associated with the art of Fly Fishing, then the May Fly is that insect. This insect has been referred to as the very foundation of the sport. Since the year 1496, the Mayfly has been known to have a great influence for the angler. Dame Julianna Burners of England described the dressings for a dozen imitations that are known to catch fish. The journal that contained this information was called Treatys of Fyshing with an Angle. In the 1600s both Issac Walton and Charles Cotton wrote on the subject and started a splurge of writings promoting the use of Mayfly imitations and this insect became the symbol associated with the art of fly-fishing. Whether you are watching a film, video, movie or reading a book, magazine, or article on Fly Fishing you will be told that the May Fly is the Holy Grail insect. There are 16 Families, 47 different Genera and over 500 North American species of this important insect but only a very small portion is of importance to the fly angler. In Maine there are over 142 species.

All aquatic insects are under a constant attack from insect predators such as; their own kind, diving beetles, salamanders, frogs, back swimmers, birds and of course the fish.

These insects have a technical name, (Ephemeridae), which translates into the phase, "lives but a day." These insects emerge from their underwater world without mouthparts and therefore can't eat. Now, you know why they live only but a day.

Another common name is Ephemeroptera, which translates to mean upturned wing.

Life Cycle
The four stages of a Mayflies life cycle are; egg (Ovum, 1 to 3 weeks), Nymph (Nymphal 11 months to 24 months with 20-30 Moults), Dun (Sub-imago 1 to 4 days) and Spinner (Imago about 1 day).

The eggs of the insect are deposited on or in water differently depending on the species. In some species the female will skim across the surface of the water in order to dislodge the eggs from her abdomen. Another species will fly across the waters surface and drop yellow or orange egg masses onto the waters surface. Some female mayflies will even use a protruding stem, leaf or other organic structure to crawl into the water in order to safely deposit her eggs at the bottom of the water column and others will actually dive into the waters surface in order to break the surface tension, then release the eggs underwater. Once the egg lying has taken place the exhausted insect will often times fall onto the surface of the water only to be taken by fish that have observed it from below the waters surface.

After time, which in some species can be as little as a few hours and in others the time can be several months, these eggs will hatch and an immature nymph will then crawl under the stones of a riffle or the medium to large rocks or boulder of a run, burrow into the silt or muddy area of the slower currents of pools or the nymph may cling to the under sides of submerged vegetation or the branches of a fallen tree along the banks or shoreline. There are even some species that will be free-swimming aquatic insects that will swim around areas of aquatic vegetation and/or any structure that has been created by fallen shoreline or banking debris. Most of the Mayfly Species have three tails but there are some that only have two. These tails are visible throughout most of the developmental stages. All will have six legs with one sharp claw on each foot. In the adult the tail can be as long as the insect itself. There are generally 10 abdominal segments with moving gills along the sides of the insect.

The crawlers are variable in size and generally inhabit areas of medium and slower currents; they consist of the prolific Ephemerellidae family, the weak-legged Leptophlebiidae family and the very small insects of the Tricorythidae and Caenidae families.

The clingers are of the fast-water Heptageniidae family and the very large Baetidae family is made up of fast swimmers, while the burrowing types are of the families Ephemeridae, Potamanthidae and Polymitarcyidae.

Dun (Sub-Imago)
This process of aquatic insects rising towards the surface is called an Emergence. Yes, I know that everyone refers to this event as a Hatch but you know the truth and that is that nymphs hatch from eggs and emerge from the water as duns. Every species has its' own emerging characteristics and time table. As the insects rise toward the surface, they become very vulnerable and fish will feed readily on them. During this emergence, fish will become very selective to the physical size, color, shape and actions of the emerging species.

Once on the surface the newly emerged Mayflies will either remain in the waters current or attach itself to a partially submerged limb or rock in order to then separate themselves from their skins or shucks - or more appropriately called exoskeleton, spread their wings, pump fluid into the veins causing the wing to strengthen in order to support flight. The Mayfly will float on the surface of the water, like little sailboats, with its newly inflated wings acting as sails being dried and blown around by the wind. This surface activity can last for only a few seconds to only a few minutes. Once the wings are dry enough and strong enough the insect will take flight. After taking flight, the sub-imago usually rests on the shoreline vegetation for 1 or 2 hours or 1 or 2 days depending on the species, while gradually going through the last molt and transforming from sub-imago into adult (imago or spinner).

Adult Mayfly
This adult Mayfly has no functioning mouth and therefore can't eat, and now you know why they, "live but a day." These Mayflies can emerge like this by the thousands and is an experience that will be remembered by any angler encountering it for the first time. These mass emergent patterns are the Mayflies main defense against its natural predators, among them being fish and birds. They will hatch in such great numbers, condensed in both time and location, that the before mentioned predators are unable to rally their troops for a mass consumption.

The sexually mature adult male spinner will mass in swarms over the waters surface. The characteristics and timing of the nuptial flight or mating swarm will vary from species to species. Once the selection and the mating activities have occurred the male will shortly die and the female will wait for low light conditions before depositing her eggs, then she too will die and fall to the surface of the water only to be consumed by a waiting fish. The dead or dying adults will then lie on the waters surface with wings spread and, at that point, is referred to as 'spent' spinners.

image : , Bruce Williams , Dale Parker

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