This time of year, the mayfly hatches are a frequent topic of conversation amongst my fly fishing friends. Tonight, I had a great conversation with a friend who fished the Green Drake hatch in Pennsylvania this weekend. The play by play of what decisions to make when selecting the fishing location, the casting positions and the fly patterns to use feels like an exciting and intricate puzzle to solve and makes for great fishing buddy stories.
The mayflies that hatch in May and June in Maryland and Pennsylvania include the Sulphur, the March Brown, the Light Cahill, the Green Drake, the Brown Drake, and the Slate Drake. Each of these bugs varies in size, color, and time of day when they hatch. As I have described previously, being present to the feeding frenzy that can sometimes happen during a hatch is a thrill of fly fishing. Here are a couple links to hatch charts for Maryland and Pennsylvania.
When I was in college at Virginia Tech, I was fortunate to take a class in Aquatic Entomology. The class was incredibly challenging, and I learned a great deal. I struggled in the class and I think I squeaked out a B-. Maybe it was a C+. But as I started my career in Environmental Science, macroinvertebrate sampling and water quality analysis became one of my primary job duties. And I really loved it. Aquatic macroinvertebrates are very important to study as they serve as the canary in the coal mine for water quality. Macroinvertebrates are incredibly diverse, have unique life cycles and requirements and are very sensitive to changes in the environment. Mayflies are one of the most sensitive of the aquatic invertebrate species and their presence typically indicates excellent water quality.
The mayfly body form and feeding styles are divided into four categories: swimmers, clingers, burrowers, and crawlers. Each of these types of mayflies has adapted to a certain range of conditions based on substrate, food sources, body shapes, and water conditions. The swimmers are most likely to be in the water column at any given time. They are typically replicated by fly fishermen as nymphs made from pheasant tail, peacock and ostrich herl. The clingers, burrowers, and crawlers are more commonly attached to the substrate of the stream and are closely resembled by hare’s ear type nymphs. This is a great article from the Frosty Fly on How to Fish Mayfly patterns.
The mayfly life cycle starts as an egg deposited on the water surface, in the water column or attached to rocks/vegetation at the water’s edge. They develop from an egg to a nymph. The nymph typically lives underwater for a period of several months to several years. Most of a mayfly’s life is spent as a nymph, primarily filtering organic material from the water and scraping algae from the substrate. Very few mayflies are predatory. The graphic below from Gilbert Rowley is a wonderful example of the life cycle of the mayfly. There are also great video resources on Midcurrent on the life cycles of mayflies.
As the mayfly reaches maturity, they must travel from the channel substrate to the surface of the water to emerge from their nymph form into an adult capable of flying and mating above the water’s surface. To aid in the ascent, the nymph’s exoskeleton becomes thinner and allows for the accumulation of gases to build up in its skin like layer, increasing its buoyancy. This stage is the moment when the insect technically hatches. A successful approach for fly fishing to emulate this occurrence in the life cycle of a mayfly is using an emerger fly. Although as you can see from the graphic, there are four main stages of the mayfly’s life when it is coupled with the water and available as a food source for feeding trout.
As the fly emergers from the shuck (or spent exoskeleton of the nymphal form) it becomes a dun. The mayfly is an ancient fly, and its upright wing position is an indication of a simplified body form as compared to the hinged wings of the stone fly or caddis fly. The dun’s wings are often described as sailboats and are typically fished using the heavily hackled Catskill style dry fly. Often mayflies only live for a day or two after they hatch into a dun. Duns are often stuck in their shucks and can’t fully emerge from the surface film of the water. Crippled dun patterns have been created to simulate this struggle of mayflies and trout will often feed heavily on these vulnerable bugs.
The metamorphosis of a mayfly from a nymph to a dun is incomplete for the purpose of completing reproduction. The duns need to molt into a spinner so that they can become sexually mature and complete the lifecycle. As the spinners mature, they aggregate into clouds above the water bodies and mate. Spinners are often different colors from the dun form and have translucent wings. The spinners cannot feed, as they have no mouth parts, and after mating they quickly die. The females will deposit their eggs in the water and are exhaustively spent, dying on the water. This life cycle stage is often fished as a rusty spinner or other spinner variation, matching the size and color pattern of spent spinners. As the spinner form dies, the mayfly will no longer move, giving itself over to the stream for subsistence of other species. It has been noted that fish become more selective as it relates to a drag free drift when feeding on spinners.
Understanding the lifecycles and body forms of mayflies is something I learned in detail in college. However, I am still learning how these life cycles impact trout feeding patterns and how to fish using different fly patterns to coincide with the natural process. The philosophy of matching the hatch is based on matching the sizes, colors, and behaviors of this life cycle to the presentations you provide and perform during fly fishing. This is incredibly challenging and takes years to understand the patterns, the timing, the casting to present the correct replication to fool a trout.
Learning this puzzle helps us continue to challenge ourselves to improve our fishing skills and to connect to our friends. Sometimes this connection is a “misery loves company” humbling conversation and sometimes you feel like the king of the world on the walk back to the car. Either way, you’re learning, growing, and have a great story to share with your friends. I sure appreciated the story tonight.