Mayflies are synonymous with flyfishing. Since the history of the sport, the two have been closely linked. The reasons why are obvious; no other insect is more available to the trout, and more noticeable to humans than the mayfly. Mayflies live almost their whole life under water. They are available to the fish as nymphs year round. When they finally emerge, they resemble small sailboats being blown around by their upright wings, lazily going where the wind and the current take them. This is the time of the hatch when mayflies are most vulnerable, and it is also the time which is treasured by flyfishermen the world over. Once they have left the water, the mayflies must go through one more change that will make them capable of reproduction. The insects then return to the water to breed and die, once again becoming food for the trout.
The stages of life for a mayfly are egg, nymph, dun and spinner.
Eggs can be deposited by the spinners in several ways; one is ovipositing, where eggs are dropped into the stream from above. Another form of egg laying takes place when the mature adult crawls onto aquatic vegetation and attaches their eggs to the plant. When the nymphs or larvae hatch, they crawl around the stream or lake bottom; it is usually a year before they are ready to hatch.
Hatching (the metamorphosis from the juvenile stage to the first flying stage) can also come about in different ways. The first is for the nymph to swim or float to the stream’s surface, where it will break open its nymphal shuck; a fully formed dun, or subimago, will crawl on to the water’s surface, dry its wings, and fly away. The second form of emergence is for the dun to crawl from the nymphal shuck onto the stream bottom, then swim to the surface as an adult fly.
A few days after the duns (subimagos) have hatched, they shed once again, their body color changes, and their wings become clear; most importantly they become mature adults capable of reproduction. This reproductive stage is called the spinner or imago. The spinners will mate in huge swarms over the top of the water.
Once they have mated, they fall dead onto the water’s surface, spent winged, like hundreds of little crosses. Due to the sheer number of flies, a spinner fall can be one of the most productive, but often frustrating, times to fish.
A nymph can be identified as a mayfly if it has all of the following characteristics:
- Gills along its abdomen
- A single claw at the end of its legs
- One set of visible wing pads
- 2 or 3 tails
Mayfly adults have the following characteristics:
- 2 sets of wings that are upright at rest
- 2 or 3 tails
- A long, usually slender, body