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In my early days as a fly-fisherman, I studied mayflies intensely because they are so important to so many aspects of the sport.
I continue to be fascinated by these beautiful and important aquatic insects. Currently, about 500 different species of mayflies occur in North America in both the flowing waters of rivers and streams and the still-water environments of lakes and ponds. Some are tiny, just a few millimeters long, while others are quite large with bodies an inch and a half or more long.
Countless fly patterns have been created to imitate the more prolific species of mayflies found in our trout streams. Many fly anglers dream of encountering a mayfly hatch on their favorite stream during a spring evening in the hopes of great dry-fly fishing as the trout pick the emerging flies from the water’s surface.
Mayflies are one of the oldest forms of insect life, with fossil records documenting their existence more than 200 million years ago. But the life cycle of mayflies is even more remarkable than their longtime presence here on Earth.
With a few exceptions, most species of mayflies have a one-year lifespan, beginning when the adult female mayflies lay their eggs in the waterway from which they came. The eggs hatch into tiny nymphs that live and grow primarily on the stream bottom. Because mayfly nymphs can be present in great numbers in so many areas of a stream or lake, they represent a most important link in the food chain for trout and other species of fish.
After living underwater for an entire year, the nymphs of a given species finally reach maturity and undergo a quick and amazing transformation into their adult stage. In simplest terms, these underwater bugs leave the water and turn into winged adults that now breathe air and can fly. And most species make that transformation in a period of seconds.
During this process, the outer skin of the nymph splits open, and the winged adult literally crawls out of its own skin. Some species of nymphs leave the stream bottom and swim to the water’s surface to emerge, while others crawl to shore or onto rocks, logs or other streamside objects to hatch.
It is during this period of emergence that trout can be spurred into a feeding frenzy that many fly anglers covet so highly. Mayflies are completely benign insects. They don’t bite, sting, damage crops or bother humans in any way. In fact, adult mayflies live only a day or two and eat nothing at all during that time because they have no digestive system.
Fly-fishermen refer to the newly hatched adult mayflies as “duns.” The duns fly from the water and retreat to streamside vegetation, where they rest before undergoing one more transition. The adult mayflies molt a day or two later into their final stage, which fishermen call “spinners.”
Male and female spinners meet in swarms over the water and mate in flight. The females then deposit the fertilized eggs into the water to produce the next generation of their species. Their mission completed, the females die soon after and often fall back into the water themselves. This so-called spinner fall can sometimes produce as many or more rising trout than the hatching duns will.
While many of the most significant hatches of mayflies occur from mid-April through early June, I have witnessed fishable hatches of them from early March until November on streams in our area. Any emergence of mayflies, however, can be a wondrous natural spectacle for nature enthusiasts and fly anglers alike. Some are a mere handful of bugs dribbling off just enough to spur the interest of the fish while a few others come off in incredible numbers. Each has its own niche in the remarkable ecosystem of any trout stream.
Last weekend, I had an amazing encounter with one of the most notable species of mayflies, the Green Drake. Green Drakes are one of the largest mayflies found in the streams of our region and generally hatch during mid to late May. Because of their size, Green Drakes have a reputation for bringing the largest trout in the stream to the surface to feed on them.
Two friends and I had the opportunity to fish a private section of Spruce Creek in Huntingdon County. The stream was already a little high and colored from rain the previous day, and a steady drizzle commenced as we pulled on our waders and strung up our rods. Given the conditions, we were happy to take some fish with wet flies and nymphs throughout the morning.
Around noon, however, a few Green Drakes started to appear. Drakes usually hatch around sunset, but the bugs apparently liked the rain and overcast and began to hatch in good numbers. By 1 p.m. every fish in the stream seemed to feeding on the newly hatched mayflies as they drifted helplessly on the water surface. And quite a few took our imitations as well. It was one of the most remarkable fishing events I had ever witnessed.