Whether or not you’ve ever been fly-fishing, chances are you’re interested with what a mayfly looks like.
Mayflies are often portrayed on the cover of books, postcards, fishing magazines and in fishing photography and are significant within the art of fly fishing and the fly fishing world.
You could in fact say that mayflies are not the most important aquatic insect in the river (caddis is far more prolific and hardier in demanding conditions) but they are essential for the summertime angler using a fly to catch fish.
Knowing a little about Aquatic Insects, where they fall in the food chain and their life cycles will help put more fish in the net, and as even more reward, will give you a better appreciation of The Sport of Fly Fishing, and what it means to the complex ecosystems of rivers and streams.
Here is a little information about mayflies in fly fishing.
What is a Mayfly?
Mayflies are fragile, aquatic insects of the order Ephemeroptera. There are more than 3000 species of mayflies. Don't feel overwhelmed.
We’ll lay down a few of the most prolific mayfly hatches that an angler should have some understanding of in an effort to help you be a little more productive on the water.
The Mayfly Lifecycle
Mayflies are aquatic insects and so spend their lives in water. Mayflies go through 4 stages of its life that includes egg, mayfly nymph, sub-imago and imago. The female of the mayfly develops an eggsack on her abdomen.
Her eggs re released into the water (4,000-8,000 per egg sack) and they sink to the bottom of the river. They attach themselves to rocks or debris, and a single egg stage may last from one day to several weeks. They eventually molt into the nymphal stage.
Mayfly larvae (known by fishermen as mayfly nymphs) have a size range from just 3-25 mm long. The typical mayfly nymph has a slender, elongate body divided into three parts: the head, thorax and abdomen.
Most mayfly nymphs have two or three long tails. Mayflies also have even smaller gills on their abdomens. The gill can be very silt and water pollution sensitive and you'll usually find these in clean water.
Given few options for escaping predators Mayfly nymphs are most of their lives. Also, they are not available as the food fish for most of their lives. The reason for this is that we can divide mayflies into 4 groups: swimmers, burrowers, clingers, and crawlers. The selected mode of growth is one which removes them from the reach of things that prey upon them.
Mayflies emerge based on the right conditions - in other words, it boils down to that whole "tipping point." The primary influence on mayfly hatches is water temperature. Incubation temperature ranges widely by species of lizard. It needs to be at least 46 degrees in most rivers. During the summer 60 degrees is a great temp for most mayflies.
Cloudy cool days produce the most hatches. The reasons that there are so many is you have cool moist weather so they can't dry their wings, which need to be erect to fly. The wetter and colder, the longer it takes their wings to dry, which is to say, that mayflies are drifting longer downstream to hungry trout.
Diggers, Trotters, Hangers, and Swimmers
Many may fly nymphs bury themselves in the substrate stream bed. This allows plenty of time for the nymphs to mature and be out of reach of predators. These clingers, swimmers, and crawlers typically occupy the bottom surface of submerged rocks.
Try computer, hand, or eye, and it gets shifted all over the place. Little wriggling water insects can be found almost at once around the undersides of the stones.
This offers not only a hiding place from their predators, but the rock is also a significant food source for the nymphs. They can scrape algae off the bottom of the rocks with its modified jaws.
The main point to understand is that for most of the insect's and fish's life, they are unavailable to one another.
It is at the very moment when time, water temperature, the time of the year, and many other environmental factors reach a tipping point. The nymph must transition from nymph to sub-imago.
Mayfly Nymphs and Emergers
This leads up to the time that the mayfly nymph comes out from under the rock or digs its way to the surface of the river. This is fish's first chance to eat the bug. The nymph must swim to the surface of the river.
To assist with the behavior, mayflies will catch air bubbles between their body and nymphal shuck. This tiny air bubble serves as flotation vehicle and propels them on their way to the surface.
Fish target in on this as well. This is why many flies are tied with a bit of flash or a clear glass bead. These extra touches mimic the air bubble on hatching.
This subset of mayfly hatches are referred to as the emerger stage. This is primarily the most critical point of the hatch for thrift fishermen a lot of the time. Trout take emergers in deep or drowned subsurface to the top surface film.
Then again, fish’s lives are under water, so most of what they eat will be under water, too. Also, you can nymph them deep, or mid water column or small dry fly just at the surface.
Furthermore, mayfly emergers in the film/ surface can be some of the easiest dry fly fishing for anglers. Trout are searching for a lazy meal. The part of mayflies’ journey that gives them the most trouble?
This intense membrane of water is formed because the water molecules are “pulling on” the next one in a three dimensional surface creating surface tension. Getting beyond the meniscus is a bear. Many mayflies don’t make it out or hang just under the surface for hours. This is the simplest for trout. Anemia doomed thing can't break cover the menscus and it's nymphal shuck are helpless game.
The Mayfly Subimago Phase
Mayflies that emerge from the nymphal shuck onto the surface of the river will reach the sub imago stage of the hatch cycle (also known as the dun stage to fisherman). The good news is that this is basically the teenage stage of an adult mayflies’ life. Dun mayflies are have not reached sexual maturity; mayflies take a long time to drift with water. They need to dry their wings before they fly off the water. Mayflies also have 2 pair of wings when fully formed. The hindwings are normally reduced and often difficult to see. This renders them easier to recognize.
Wings are upright and vertical. A fly fisherman, drinking them in, “Depending on what type of mayfly nymphs are hatching, they look like little sailboats floating on the surface of the river. This is the complete opposite of caddisfly larvae or stone flies hatching. Both of those insects have wings that lie flat horizontally.
This is the second fisherman and trout have to be vulnerable in the right place. Also weather conditions of the cloud cover and cool air or the moisture in the air can extend the process. That should equate to longer periods on the water and more time when big fish are feeding and more prolific mayfly hatches.
The Adult Mayfly
Once the wings of the mayflies are developed and dry, they fly from the water to plants adjacent to the water. The final larval molt will take place inside the CSB, where they will be for 24-48 hours, continue on to reach sexual maturity and become a mature adult.
It is interesting note that the mature mayfly is unusual because it is the only insect that undergoes a molt after it has developed its wings! This is the last part of the life cycle of the mayfly, the adult mayfly, or the imago stage, and mating.
The final phase of the mayfly’s life cycle will be familiar to any fisherman who has spent time on a river during mayfly hatches–the massive swarms of mating mayflies that congregate in swarms above the river’s bushes. It can occur at any time of day, but is most commonly found in the later part of each. Anglers using fly, also commonly call the mayfly adult a spinner.
Then she, with an egg sack fully developed at the tip of her abdomen, will re-emerge to the surface of the river and deposit that egg sack. In one final act of depletion, she collapses onto the water's surface utterly "spent" of life, and succumbs. This will be the last opportunity for fish and to take advantage of the hatch. Lifeless pieces of food floating downstream are irresistible.
Final Thoughts
Mayflies are an excellent food source for trout therefore they are a complex part of the trout ecosystem. When a fly fisher is working a river during a Mayfly hatch, it is trout catching season. Rivers and streams are pounding with the spring runoff and the trout are hungry to feed and opportunistic for an easy meal.
During the Mayfly hatch is the best time, and it will allow you to catch many, many trout and have a blast doing so because the trout’s food is so prevalent. Trout are less wary, so fly-fishing just got easier than usual.