Of all the insects that you will learn to love when it comes to fly fishing, the mayfly is one of the prettiest and most interesting. The mayfly, or shadfly, is an insect belonging to the order Ephemeroptera, which refers to the Latin words for “short-lived” and “wing”, referring to the fact that these insects have a short lifespan. Also in this family are the dragonfly and the damselfly. Not only are these insects all beautiful to look at, but they also form an integral part of the diet of a majority of freshwater fish species.
Life cycle and metamorphosis
The immature stage of the mayfly, known as the naiad or more commonly the nymph, lives for around a year in freshwater, generally under rocks, in decaying vegetation or sediment. Gradually, the nymph develops and changes, undergoing moults and developing dark wingpads in the later aquatic stages. After acquiring fully functional clear, membranous wings, the mayfly moults one final time, with this first winged stage, commonly referred to as the “dun”, being exceptionally brief and lasting but a few hours before the mayfly becomes a fully fledged adult. Unlike the nymph and other aquatic stages, the mature form of this insect lives for only a few minutes, hours or at the most a day or two. Basically, the adult lives long enough to ensure reproduction occurs, and doesn’t eat or perform any function other than reproducing. Eggs are laid on the water and the nymph hatches, beginning the lifecycle again.
Mayfly as trout food
There are several specific stages of the life cycle of the mayfly that often make up important components of the diet of a trout at specific times. Nymphs live underwater, and are a common food source for trout in rivers and streams. As these nymphs live predominantly in silt, under rocks, and within rotting plant matter, trout feed on them underwater, without rising to the surface. On the other hand, the first winged or “dun” stage of the mayfly is when the insects are found at the water’s surface. Duns are an incredibly important part of the diet of lake, stream and river trout, with fish rising to catch these insects in the morning, afternoon and evening.
The progression of the mayfly from nymph to dun often occurs in specific conditions, such as warmer weather. This is known as a “hatch”, and results in thousands of nymphs metamorphosing into duns all at the same time. During such times, trout often become distracted and won’t focus on any other food source, feeding only on duns. If you have anything else on the end of your line, you probably won’t be successful.
Artificial imitations of mayflies
As both nymphs and duns provide important food for the trout, these are easy targets when it comes to tying flies that appear similar to these insects. Nymphs are usually tied in dark colors, on a range of hook sizes, usually #8-#14. As nymphs are required to sink, these flies are often tied with weights attached, usually in the form of a gold or silver bead attached to the front of the fly. When it comes to imitating duns, flies must be able to float, as these insects are found on the surface of the water. Imitation duns are tied using feather hackles to both imitate wings and also ensure that the fly floats. Trout feeding on duns are incredibly exciting to fish for, as you can watch the fish rise in real time, cast your fly right in its line of sight, and watch it swim up to take your fly.
Mayflies as a species are a unique and interesting insect, and from a fly fishing perspective, a hatch certainly can ensure that you have a great day on the water!
Tying a Spent Gnat (MayFly)