Mayflies

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.

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.

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 Mayfly goes through an incomplete metamorphosis, which simply means that the insect misses one of the underwater insect stages common to most other aquatic insects. This Mayfly Life Cycle starts with adult female depositing eggs in or on the water. The eggs then fall slowly onto the lake or stream bottom and in time will develop into an aquatic creature called an immature nymph. These nymphs are classified into four basic groups: Burrowing, free-swimming, crawling and clinging. The Burrowing nymphs like areas that have a either slow or very calm current with a soft bottom made up of rich silt, fine sand, decayed organic debris and marl bottoms of pools, eddies and quiet stretches of river and streams, as well as, the firm bottom-muck of cool lakes and ponds. The free-swimming nymphs will inhabit areas where there is plenty of natural structure such as, aquatic vegetation and heavy aggregate bottom areas. Some fast swimming nymphs will also inhabit a riffled area. The Crawling nymphs will inhabit areas of moderate to fast current. Most species have weak legs and are very poor swimmers. They will inhabit the moderate currents among vegetation, gravel and the rubbled bottoms of the water column. Some will even exist in the riffled waters and also the faster current of runs.

Clinging

The Clinging nymphs love the faster and highly oxygenated waters of the riffles. This nymph has a classic flattened appearance with their heads and bodies designed for the faster currents. Nymphal life cycles can range from between 3-4 weeks to 2.5 years depending on the species of the insect. This process skips the common Larval Stage that most other aquatic insects go through, thus the incomplete life cycle that I mentioned earlier.

These Mayfly Nymphs can spend as little as six (6) months or as much as the next two years (give or take a month or two) Borrowing, Crawling, Clinging, and Swimming around the bottom of the water column. The period of time spent as a Nymph will depend on the specific species of the Mayfly. For instance the Baetis Mayfly can complete up to three life cycles in a years time. However, the Hexigenia limbata mayfly will require slightly more than two years completing its life cycle.

Swimming

Nymphs will feed on algae, diatoms, plankton, vegetable or organic matter and microscopic organisms. As the aquatic insect grows, the outer skin, which serves as a skeleton, limits the ability of the nymph to enlarge. In order to continue to grow this insect must from time to time, shed or molt the hard exoskeleton.

Once the hard shell has been removed the insect will secrete a fluid from its epidermal cuticular membrane, which will harden into another exoskeleton in which the nymph can grow.

The period of time between these molts is called an "instar" and many species will molt some 20 to 30 times before emerging into the air-breathing world above. Between the molts and during the instars the nymph is very vulnerable to its principal animal, bird, fish, amphibian and insect predators such as: dragon fly nymphs and adults, diving beetles, frogs, back-swimmers, salamanders, swifts, swallows and phoebes. The mayfly nymph will spend nearly 95% of its entire lifespan below the waters surface.

Burrowing

When the Nymph reaches maturity it will transform into a 'sub-imago'. The sub-imago is what we see emerge or hatch from the Nymphs. They are not an adult but are fully winged. This insect is called a Dun and must go through one more molt before becoming a sexually mature, "imago."

Now, the year has gone by and the Mayfly Nymph along with tens of thousands of other Mayfly Nymphs begin to instinctively desire to leave their aquatic environments and rise to the air breathing world above. What really triggers this event can be debated by those much wiser that I. There seem to be two schools of thought allowing us to consider two options. These options are that the processes are either biological or environmental. The biological explanation is that during the last few weeks of the mature Nymphs life stage, gasses will form between the Nymphal Shuck (outer shell) and the immature Mayfly. Over time the gas will greatly affect the insect's ability to remain below surface and the gas will create positive buoyancy sending the insect to the surface whether it likes it or not. The other real factor is the water temperature. When an area of water reaches a temperature of 50 degrees and maintains that temperature range for three consecutive days, there will be a Mayfly hatch. You could even include the two by allowing the gases to expand as the water temperature increases. In any event, we all know that in the spring, the fly angler will eagerly await this ritual.

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).

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.

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