In most areas where trout live, four orders of aquatic insects comprise a majority of the food the fish eat. The orders are mayflies (Ephemeroptera), stoneflies (Plecoptera), caddis flies (Trichoptera), and midges (Diptera). At one time or another ardent fly fishers experience hatches of aquatic insects that give the anglers indelible memories of fantastic fishing.
Perhaps the most written about insect hatch in the United States is the blue-winged olive mayfly. Blue-winged olives have a genus name of Baetis and belong in the family Baetidae. Most of the blue-winged olives hatch in the spring time; you might say they are a May fly.
Mayflies have a three-part life cycle: fertilized egg, nymph and adult. A hatch is when the mature nymph swims to the surface and sheds its nymphal shuck and becomes an adult. The adult mayflies undergo another molt, mate, and the females return to the water to lay their eggs. The female mayflies at this stage are called “spinners.”
Most mayfly species lay their eggs by landing on the water, spreading their wings perpendicular to their bodies and driving their ovipositors through the water surface and extruding the fertilized eggs into the water. The eggs are slightly denser than water and settle down to the bottom.
Freestone streams in the Sheridan area have blue-winged olives hatching as early as late March with the peak hatches usually occurring in May. The blue-winged olive nymphs are quite common in streams and are frequently eaten by trout and other fish. Nymph fly fishers can imitate the Baetis nymphs with such popular patterns as Gold-Ribbed Hare's Ears, Pheasant Tail Nymphs and Quill Nymphs in sizes 16 and 18.
Several dry flies work quite well on the blue-winged olive adults: Blue Duns, Olive Compara Duns, Parachute Adams, Students, and Blue Quills, to name a few. Again, the size of the fly to fish is either 16 or 18.
A few years ago I was guiding a couple of anglers on the Bighorn River and noticed that there was quite a spinner fall of blue-winged olives. I pulled out my dry fly box and started to rummage through it as I looked for a blue-winged olive spinner pattern. After a fairly thorough search I discovered that I didn't have any spinner patterns. I thought, “After all the years guiding on the Bighorn, why don't I have a blue-winged olive spinner?”
We managed to make do with a pattern that Frank Johnson had invented — the Student. It is a sparsely tied CDC pattern with a few strands of dun CDC for a tail, an olive thread body, and a dun CDC wing.
The following day I was guiding a knowledgeable angler, Skip James. When I mentioned that I couldn't find a spinner blue-winged olive pattern he replied, “Blue-winged olive spinners swim down to lay their eggs.”
I didn't dispute what James said, but I doubted it. All my education said mayfly spinners landed on the surface and laid their eggs through the surface film.
I mentioned to my son, Clint, that James had said that blue-winged olives swam to the bottom and he verified the statement. “Dad, I learned that 10 years ago from Barry and Cathy Beck,” he exclaimed.
Still unwilling to accept even what my son said, I emailed my friend, Dave Hughes. Hughes is an excellent writer and qualifies as an aquatic entomologist. Hughes emailed me back to verify that blue-winged olives do swim or crawl down to the bottom to lay their eggs.
When I accepted the information I began to make some conclusions about previous fishing experiences. I used to have excellent luck with a pattern, RS-2. I was told that it was an emerger pattern for blue-winged olives and fished it in riffles that dropped into holes or runs. The pattern was deadly just as it came off the shelves in the stream and was very good at predicting strikes on the floats. In retrospect the fish weren't taking the RS-2 as an emerger but as the egg-laying spinners heading down to the bottom.
I also started to note that blue-winged olive spinners landed on me when I was wading and crawled down my waders into the water, just like black caddis do later in the year.
The blue-winged olive hatches have started and will continue into June so if you get out make sure you have a variety of flies to imitate the mayfly nymphs, adults and spinners. Regardless of the flies you chose, you should have good luck, and watch for those spinners crawling down your waders.