Mayflies, Ephemeroptera, are an important order of insects to many fish, but particularly to trout. I have read that the four most important aquatic insect orders for trout food are mayflies, stoneflies (Plecoptera), caddis (Trichoptera) and midges (Diptera).
The word Ephemeroptera can be broken down into two root words: the Greek word ephemeros, meaning short-lived, and pteron, meaning wing. Mayfly adults, in general, live only a day, while the nymph lives a year. Mayflies aren’t only present in the adult form in May, there are species of mayflies that hatch from March into October. I have even seen adult mayflies floating down the river and through my duck decoys in November.
Most species of mayflies live in moving waters like streams, rivers and creeks. A few species live in standing waters, like lakes and ponds, and these species can be extremely numerous. A hatch of the mayfly Hexagenia in Lake Erie was once so immense that the cloud of insects was reportedly picked up by Doppler radar.
While our area doesn’t have Hexagenia, it does have many other genera of mayflies. At this time of the year, perhaps the most noticeable aquatic insect is the blue-winged olive mayfly, Baetis tricaudatus. The blue-winged olive mayfly hatches in most freestone streams in April and May.
There are spring blue-winged olives and fall blue-winged olives, but let’s just concentrate on the spring ones for now. Blue-winged nymphs feed on algae and live on the large gravels or cobblestones in a river or creek. These nymphs crawl about and hang on pretty well, but sometimes they lose their footing and are swept away by the current. Oftentimes the nymph is gobbled up by a predatory fish, but some manage to gain a foothold on a new rock.
Many nymph fishermen imitate the blue-winged olive nymph with fly patterns like the pheasant tail nymph, gold-ribbed hare’s ear, quill nymph, Baetis nymph, Downey wonder nymph, and Juju Baetis nymph. All the patterns are pretty effective and enable you to catch a fair number of trout for a few months prior and during the time that the blue-winged olives are hatching. (A hatch refers to when the nymphs swim to the surface, shed their nymphal exoskeletons and fly off as adults). Keep in mind that for a particular stretch of stream, hatches may take place for several weeks, but the peak may be somewhere in the middle of the time span.
Prior to the hatch, dead drifting the nymph through a run or pool will work passably well. During the hatch, a nymph fisher can have great results by allowing the nymph to rise up at the end of the dead drift, thus simulating the real insect swimming up to emerge. Oftentimes the strikes that an angler will get are quite hard, and it is not unusual for the fish to break off the fly with its take.
When the blue-winged olive nymph swims to the water surface, the exoskeleton will split at the top of the thorax; the adult insect crawls out of the exoskeleton and pumps blood into its wings and flies off in five to 10 seconds. The adult insect looks like a little sailboat because it has upright wings. The wings are more of a dun gray than blue. Often there is a glitch in the insect emerging from the exoskeleton or when the wings are unfurled: a gust of wind or some deformity might prevent the mayfly from fully developing, so a cripple results.
Trout feed heavily on the cripples because they are caught in the surface film and can’t go anywhere. Cripples are a certain meal while the fully developed adults can fly away at any second. In a typical mayfly hatch I would estimate that 15 to 30 percent of the mayflies are cripples. Windy, rainy conditions drive the cripple rate to the upper end of the estimate.
During the hatch, typical dun mayfly imitations work well. Some examples are blue duns, CDC Baetis, thorax Baetis, sparkle duns, parachute Adams and students. Cripple patterns also work.
After the blue-winged olive leaves the water, it will land somewhere and molt. After that the mayflies fly off to mate in the air. The male mayflies have long forelegs that grasp the female. One unusual trait of mayflies is that they have paired genitalia — the males have two penises and the females two gonopores.
After mating, the females return to the water to lay their eggs and then die. In most species of mayflies the females land on the water, spread their wings perpendicular to the body and then drive their ovipositors through the surface film and extrude their eggs. The blue-winged olive mayfly is unusual in that the female swims to the bottom of the stream to lay its eggs — a fact that I only learned last year. The trout will gobble the swimming mayflies just as avidly as they ate the emerging nymphs. The RS-2, which I had fished as an emerger pattern for years, is actually a swimming spinner pattern. Whatever the RS-2 imitates, it catches fish.
This weekend’s weather is supposed to be pretty springlike for a change, with temperatures in the mid- to upper-60s with a slight chance for rain. So maybe it’s time to get out and try fishing one of our tailwater rivers. You can bet the blue-winged olives will be there, and the trout will be eating them.