Bighorn River Baetis

It’s that time of year. Blue Wing Olive mayflies are hatching and anglers are enjoying some great dry fly fishing. Large numbers of Bighorn River trout utilize these insects throughout the spring and fall as a major food source. But cracking the Baetis code can be challenging at times. It’s important to understand some of the science behind these insects. Technical information of this type is valuable not only for catching more fish, but also for impressing your friends and members of the opposite sex.

First of all, the common name of these prolific little mayflies is Blue Winged Olives, or for some just “Olives.” I haven’t noticed that their wings are blue, but rather a pale gray, and their bodies tend toward olive or olive gray hues. Many anglers refer to them as Baetis, which is the genus of this mayfly. For those of you who have forgotten what you learned in high school biology class, all insects, and indeed all creatures on earth, are classified by scientists into a series of sets and subsets depending on how closely related they are. This classification structure is called taxonomy, not to be confused with taxidermy. Taxidermy classifies all its creatures into the “dead and stuffed” category. But with taxonomy there’s Kingdom, Phylum, Class, Order, Family, Genus and Species. I guess they even throw in Suborder, Subfamily, and Subspecies at times, just because these scientific folks are looking for things to do.

So to break down the Bighorn River, Blue Winged Olives we have:
Order: Ephemeroptera (mayflies)
Family: Baetidae
Genus: Baetis
Species: Tricaudatus

I’m not saying that Tricaudatus is the only Baetis species we have in the river, but certainly the most important. One of the common names for the Baetidae family of mayflies is “small minnow mayflies.” The nymphs are swimmers and are streamlined in appearance. They can live in a variety of habitats, but alkaline rivers with abundant, aquatic vegetation seems to be ideal. They are multibrooded, meaning they produce more than one generation in a year. This is why the Bighorn has both spring and fall Baetis hatches.

Just to review the life cycle of these insects, after eggs are oviposited (laid) in the water and become attached to the substrate (substrate is a fancy name for river bottom, and I use the word quite often to impress people) the nymph begins to develop and grow. Actually, “nymph” is the common name for the more scientific, “larvae,” but we’ll stick with nymph. Ultimately the day arrives when the nymph approaches maturity, whereupon it rises or swims to the surface where it sheds its old exoskeleton and becomes a subimago, or what we fly fisherman refer to as duns. This is a very exciting time for the insect as it has heard many rumors about the world above and it’s time to find out what it’s all about. It’s kind of like a young person going off to college, but without the drugs, sex, and rock and roll. Well, at least the drugs and rock and roll. As exciting as this time may be, the journey to the river’s surface is fraught with peril, as both trout and birds seek to ambush our little insect and cut the whole cycle-of-life drama short. At this point, the top of the nymph’s thorax has split and the dun crawls out onto the surface. If all goes well, after a few flutters of the wing to dry things off and to test these new appendages, the dun takes flight, winging his way joyfully skyward, exhilarated by the experience of flight and the possibilities of life in this new world. Whereupon he is eaten by a barn swallow. Nobody said this was fair.

While this nymph-to-dun process doesn’t take long, this is a vulnerable time for the insect. Hungry and insensitive trout will often take advantage of the situation. This is why savvy anglers often fish “emerger” fly patterns that imitate this vulnerable, transitional stage. There are many different types of emerger patterns. Some people fish a floating nymph that has a little ball of poly dubbing on the top of the thorax to imitate the unfolded wings of the dun. Others use a pattern such as the RS-2, a nymph invented by Denver fly tier, Rim Chung. The muskrat dubbing body has the dark silhouette needed, and it works well fished deep or in the film. The RS-2 has taken thousands of Bighorn River trout over the years. The Flashback Quill Nymph is another good Baetis pattern. The dark, slim profile with just a little flash is the key to its success. And then there is the Student, Frank Johnson’s incredibly effective pattern. The Student is more of a stillborn dun imitation and it is proof of the “simple is better” way of thinking. As a general rule I avoid flies that take more than 45 minutes to tie, and attempt to mimic a bug’s facial expressions. The Student is a modest little pattern that gets the job done, usually better than anything else.

The CDC Baetis Sparkle Dun is often my fly of choice when it comes to imitating a dun. Tie these with natural, dark dun CDC as the darker stuff is more visible on the water than a lighter gray color. Use Fly Duster or a similar type of powder desiccant when the fly becomes waterlogged. The use of these powders is essential for taking a multiple fish on CDC fly patterns. Make sure to buy powder that has a brush attached to the cap. The brush allows you to work the powder into the CDC far better than the other powders that you shake the fly in. And for you big-city, Studio 54, jet-set types, remember that this powder is not to be snorted.

I often trail a Student behind the Sparkle Dun. I like to keep them about 20” apart. If you can’t catch them on this rig I strongly suspect that the problem is the Indian, not the arrow. Depending on the conditions, a traditional Blue Dun pattern also works very well. I like to fish a Blue Dun when there’s a breeze and the duns are being blown around a bit.

Back to the biology lesson: After the subimago/dun flutters off the surface of the water and is lucky enough to evade winged predators, it finds refuge in streamside foliage. Here it rests for a time, and within a few hours it (it has no functioning mouthparts, so it can’t eat or drink) sheds its exoskeleton once more as it is transformed into the sexually mature imago, or spinner. After this, the insect waits for the right time, calm mornings and evenings usually suffice, and goes in search for a mate. Baetis spinners, with their almost transparent wings, gather in a cloud, begin their mating dance, and attempt to “hook up.” Needless to say, this is also a very exciting time for our little insects, but nobody has told them that after the mating frenzy they will fall lifeless to the surface of the water, or at least the females will. If you care to examine this situation closely with a magnifying glass, you will find hundreds of these dead, sexually-fulfilled mayflies with tiny little cigarettes clenched in their tiny mouths. Okay, so that’s not exactly true, but they do die and the trout once again take advantage of the situation. A spinner fall is one of those events that it might be easy to overlook, as they often occur in conjunction with another hatch. You have to pay attention out there.

When the insects fall on the water, they do so with their wings outstretched. This spent-wing profile is what the fish are looking for. Bighorn River Baetis spinners are a rusty olive color (see picture). A very effective pattern utilizes a quill abdomen, dubbed thorax, and sparkle poly wings. You can also substitute CDC wings. Some anglers tie burnt-wing patterns which are very realistic, but I find they tend to twist fine tippets, and fine tippets are important when fishing spinners. Another good pattern is a parachute fly with appropriate color and grizzly hackle. Grizzly hackle is a good spinner wing color. I usually trim the parachute post down a bit. Parachutes are easier for the angler to see than classic spinner patterns.

We should enjoy Tricaudatus hatches throughout May and the first half of June. They will reappear in the fall. Cloudy days can provide epic dry fly fishing. Now is the time of year to be here.

Baetis Spinner – Jim Schollmeyer photo