Fly Fisherman Throwback: Baetis: Memorable Days from Arizona to Massachusetts

Editor's note: Flyfisherman.com will periodically be posting articles written and published before the Internet, from the Fly Fisherman magazine print archives. The wit and wisdom from legendary fly-fishing writers like Ernest Schwiebert, Gary LaFontaine, Lefty Kreh, Robert Traver, Dave Whitlock, Al Caucci & Bob Nastasi, Vince Marinaro, Doug Swisher & Carl Richards, Nick Lyons, and many more deserve a second life. These articles are reprinted here exactly as published in their day and may contain information, philosophies, or language that reveals a different time and age. This should be used for historical purposes only.

This article originally appeared in the July 1984 issue of Fly Fisherman magazine. Click here for a PDF of the print version of "Baetis."

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Autumn is a season of change, a time when many fly fishermen put away their dry fly tackle and pursue spawning trout with sturdy rods and big streamers. This is an effective tactic, with its own charm, but I prefer to follow hatches and take my fish on the surface with more delicate tackle. This is no quixotic illusion on my part, for even in the fall I can find large trout rising to copious mayfly hatches. Take, for example, a windy October day several seasons ago in Montana.

Mayflies were emerging from the tail of a choppy riffle and the stiff breeze concentrated them over a shallow shelf along the bank. There were fish, large fish, taking the tiny olive duns from water no more than six inches deep. I picked out what I thought to be the largest fish and drove my first cast into the wind. It was a poor cast, crashing down several feet wide of the mark, but all was not lost. A good trout was feeding in its line of drift and he took the fly without hesitation. When I set the hook, the fish tore upstream, its back cutting a broad swath across the ankle-deep shelf. It reached deeper water and slowed briefly, then jumped and reversed direction, using the powerful current to drain my reel of its line. Three busy minutes later, and 50 yards downstream, I led the fat rainbow over my net. A 16-inch fish may not be a trophy on this blue-ribbon river, but it was a splendid reward for a bungled first cast. It was an auspicious beginning to a glorious day, and more than 30 trout–the best a 20-inch rainbow–followed it into my net before the hatch ended four hours later.

For All Seasons

Most experienced dry-fly anglers have a favorite hatch. Salmonflies, green drakes, Hendricksons, and tricos all have their champions, and each is worthy of an angler's affection. But my favorite hatch, for reasons that soon will become evident, is the emergence of mayflies of the genus Baetis. These were the little olive mayflies that brought fish up that bright October Montana day, and they have provided me with memorable days on rivers from Arizona to Massachusetts. I've encountered fishable hatches on mountain rills and on big valley rivers, on alkaline spring creeks and on acidic bog streams, on cold and on warm days, on dry and on wet days. I've fished their hatches on New Year's Day and New Year's Eve, and on many days between. They are probably the most ubiquitous mayflies in American trout streams, and in some streams–particularly in the Arctic and those above treeline in the West–they may be the only mayflies present. Baetis is truly a hatch for all seasons, a mayfly at home in almost every North American trout stream.

The genus Baetis is distributed virtually worldwide, the only notable exception being New Zealand. There are about 50 species in North America. I say about, because the taxonomy of this genus is in a state of flux. Edmunds, Jensen, and Berner's The Mayflies of North and Central America, published in 1976, listed 59 North American species, but a more recent review published by Morihara and McCafferty in 1979 lists only 39. Some entomologists regard the North American species of Pseudocloeon as indistinguishable from Baetis, and if we accept this view, which makes sense from an angler's standpoint, a few more species should be added to Morihara's and McCafferty's list. Fifty species is a reasonable estimate.

Baetis nymphs are streamlined, reflecting their strong swimming abilities, and they move from rock to rock or from weed to weed in quick, rapid bursts. Most have three tails, although in many the middle tail is short, and in others it is absent. Their prominent antennae are usually at least three times as long as the head. Most are dark, some shade of olive or brownish-olive, although some are very pale olive. They are most abundant in well-aerated riffles with coarse gravel bottoms, but they are also common in weed beds and rocky runs. Some species are found in stillwaters, but fishable hatches occur most often in moving waters.

Baetis duns and spinners have two tails, and adult males are characterized by an unusual divided eye. The hind wings are reduced; in some cases they may lack veination and in other cases they may be absent. The absence of the hind wing was once thought to distinguish Pseudocloeon from Baetis, but this distinction doesn't hold, at least in North America. The hind wing has been lost in several evolutionary lineages of the family Baetidae, and absence of a hind wing is not sufficient to separate the two genera. Besides, there is at least one Idaho species in which the male has hind wings and the female lacks hind wings. But these are details best left to entomologists; I doubt that even the most sophisticated trout cares.

Baetis duns usually have gray wings and bodies with an olive cast, but the gray in the wings can range from the deepest plumbeous to the palest pearl and the olive cast on the body shades range from dark brown to almost yellow. The spinners are not quite as variable; the ones I've seen have had hyaline wings with dark brown or pale greenish­olive bodies, but I'm sure they come in other shades I've been too preoccupied to notice.

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Anglers think of Baetis as small mayflies, and this is usually true. Most Baetis hatches are best matched with a #20 fly, and some of the pale species require a #22 or even smaller. But there are larger forms: the mid-October hatch of Baetis tricaudatus on the lower Henrys Fork can be matched with a #16 imitation.

I've always had an interest in the details of fly fishing entomology, but I've tried not to let it interfere with my fishing. In discussing Baetis, a wealth of technical detail may obfuscate more than clarify. It seems more "scientific" to tell someone you fished an imitation of an emerging Baetis vagans rather than admit you used a #20 Olive Floating Nymph, but the latter statement would be far more informative. For one thing, Baetis vagans, despite its use in angling entomologies, is no longer a valid species name (Morihara and McCafferty regard it as identical with Baetis tricaudatus). Even the correct scientific name would give few useful hints because Baetis tricaudatus duns range in color from a pale olive brown to a dark earthen brown and can be matched by patterns tied on hook sizes from #16 to #22, depending on where and when you find them. Entomologists accept this variation when they assign scientific names, but selectively feeding trout are more concerned with the behavior, size, and color of hatching mayflies than with their evolutionary pedigrees. Fortunately, a Baetis is a Baetis in North America, and while they may differ in size and color they share most other characteristics of importance to fly fishers.

Dense Hatches

Baetis are important trout-stream insects for many reasons. Not only are they widely distributed, but they also reach astounding population densities. Thousands of nymphs may inhabit each square foot of stream bottom in good trout streams. Baetis nymphs can reach such high densities because of their food habits. They feed on plants and detritus and thus, occupy feeding niches close to the base of the food chain.

In streams with short growing seasons-at high elevations or high latitudes-there may be only a single species and a single annual emergence. In most trout streams, however, the thousands of nymphs per square foot include several species, and many species of Baetis have several broods each year. A common pattern is to have one brood emerge early in the season and another late in the season, but on streams with uniform conditions (like spring creeks and tailwaters) there may be emergences throughout the year. So at any given time, a wide range of sizes of Baetis nymphs are available to trout.

Baetis nymphs are major components of passive downstream drift, usually occurring during low light periods, often just at dusk, and trout often feed heavily on the suddenly available nymphs. Although Baetis nymphs are important items in a trout's diet, especially during these periods of behavioral drift, I rarely fish an imitation blindly. Fishing a tiny nymph in these conditions requires more faith and patience than I can usually muster, and there are better flies to try during drift periods–larger patterns that are easier to fish and have more appeal to bigger trout.

Fishing A Baetis Hatch

The best time to fish a Baetis nymph is during a hatch, casting to trout you can see. Larger trout often are reluctant to come to the surface even though they are feasting on the hatch, and a sunken nymph may be the best way to engage their attention. Sight-fishing a nymph is an intriguing blend of hunting and fishing, one that pays off in larger-than-average fish. Spotting a nymphing fish during a heavy Baetis hatch is not as difficult as it sounds, and with practice you can do it even in relatively broken currents. Look for movement near major drift lanes or "nervous water" in the shallows. Fish feeding on the nymphs during a hatch move frequently, and it is this movement that you must look for.

When I spot a nymphing fish I'll try a dead drift or two, but since the nymphs are active during a hatch, a carefully worked imitation usually is more effective. I cast my fly well upstream, generally from a position across or slightly upstream, and allow it to drift freely near the bottom. When it approaches the fish, I tighten the line and lift my rod slightly. The nymph darts forward and upward, and as often as not the trout will move to grab it.

It's hard to beat the standard Sawyer dressing of the Pheasant Tail Nymph if you want to mimic Baetis nymphs. This is a dark fly, so in some situations a paler pattern may be more successful. A pale olive or chartreuse dressing, suggested by Fred Arbona, works beautifully. Regardless of the pattern, the nymph should be dressed sparsely, in keeping with the slender build of the naturals. Hackle is unnecessary because they swim with their legs pressed against the body. In order to keep the silhouette slim, I don't weight the fly directly. If I want it to sink faster, I use tiny split shot or lead sleeve a foot or so above the fly on the leader.

Baetis emergences generally occur during midday. Many anglers regard dark rainy days as ideal Baetis weather, but I have enjoyed spectacular hatches on bright afternoons, especially during the fall. Once the hatch is underway, trout may feed preferentially at the surface. There is an excellent reason for this: The water's surface is a two-dimensional barrier to the emergence of the dun, and both struggling nymphs and recently emerged duns concentrate at this level. A feeding trout need monitor only two dimensions; it can ignore the third dimension of depth and still feed efficiently. Baetis duns emerge in both gentle and rough currents.

Some species require turbulence for successful emergence; although excellent hatches come off in rough water, the best hatches seem to occur in riffles and runs with choppy, but not violent, surfaces. The emergences are easy to spot on calm surfaces, but it is easy to miss the little duns in fast water. Trout rarely make such an oversight, and some of the best Baetis hatches I have fished have been in big, fast western rivers. Trout move out of the deeper holding water during these hatches and I have often seen two- and three-­pound trout feeding in water only three or four inches deep. This is where most anglers wade, so it pays to take a close look before you get your feet wet.

Patterns and Presentation

My favorite fly for taking trout feeding at the surface during a Baetis hatch is the Floating Nymph, originated by Swisher and Richards and championed by Rene Harrop. It's a superb fly, simple to tie once you get the hang of forming the little polypropylene ball, and reasonably durable. I grease them and fish them dead-drift over rising fish–the pale gray poly balls are surprisingly easy to follow even on the roughest currents. This is dry fly fishing all the way, and to be consistently successful you must strive for fly-first, dead-drift presentations. Approaches from across-stream or downstream and a leader designed to fall loosely on the water will help immensely in achieving these presentations. Fish will occasionally key on the wing silhouette of Baetis duns, and you will sometimes run across a trout that thoroughly inspects each fly. It rejects pattern after pattern before finding one that meets the muster. These selective trout, the kind you always read about, are sometimes found in numbers during Baetis hatches.

The Yellowstone River above Hayden Valley is one of the most popular fisheries in the country. The cutthroat are usually more than willing to forgive errors of pattern and presentation, and the stream can be a beginner's delight. I've heard many experienced anglers complain about how easy they are to catch, and every now and again I'll take one of these critics to fish a late September Baetis hatch on the flats above Buffalo Ford. This hatch brings out the best in these fish, and a Yellowstone cutthroat sipping Baetis duns in flat water is a challenge worthy of any fly fisher. These fish can be incredibly selective to presentation, pattern, and size: the only pattern I have found that takes them consistently is a Paradun tied with a duck-feather wing and no more than three turns of tiny hackle. Just because these fish are particular during this hatch is no sign of sophistication; the same fish that inspects and refuses the most elegantly dressed No-Hackle or Thorax Dun on a 7x tippet may eagerly engulf a #6 olive Woolly Worm dangled on a 3x leader a few minutes later. But that's beside the point; if you play the game fairly they accept no errors.

Baetis spinner falls are rarely as important as the duns, but if you're not paying attention they can sneak up on you. Early and late in the season they may occur at the same time the duns are emerging, in the middle of the day when the air is warmest. A fish that consistently refuses a Floating Nymph may be one that is feeding selectively on spinners, and a change to a small Rust Polywing Spinner will often do the trick.

An extremely effective tactic for trout that resolutely refuse a dry fly during a Baetis hatch is to use a sunken spinner pattern. The females of some Baetis species crawl underwater to deposit their eggs and are swept away by the current once their task is done. A small Polywing Spinner, dressed on a wet fly hook and weighted with a tiny split shot, will often take fish that seem uncatchable. The sunken spinner is effective even when females deposit their eggs on the surface. The spent spinners get dragged under by twisting currents, and fish relish these helpless tidbits drifting in the riffles.

Baetis hatches will rarely bring up the largest fish in a stream, even when they blanket the surface, but a good hatch will usually interest decent-sized fish. On the Deerfield in Massachusetts this might translate into a 14-incher, on the Beaverkill in New York or Falling Springs in Pennsylvania it might mean a 16- or 17-incher. The largest trout I've ever taken during a Baetis hatch was a sausage-fat six-­pound rainbow from the Henrys Fork, and I've seen fish larger than this feeding on Baetis hatches on the Bighorn. I usually take these big fish on an ant or beetle imitation, but were it not for the Baetis enticing them to the surface, they might not so willingly have ventured into dry-fly range. A six-pound trout is hefty baggage for a #20 fly (the main reason I prefer a more substantial ant when the major players show up), and you'd do well to forget 3x fine dry fly hooks if you're ever faced with big fish. I used to use a short-shank Mustad hook (94843), which allowed me to dress a #20 fly on a hook with the gape of a #16, but these hooks are hard to come by, and they were always a bit on the weak side. This past fall, Craig Mathews suggested I try Partridge Captain Hamilton Wet Fly Hooks for small dry flies, and they have worked well in the short time I've been using them. They are slightly heavier than standard Mustad dry fly hooks but they are far more resistant to straightening. They also have slightly wider gapes and slightly shorter shanks than Mustads, and a #18 Partridge is about the same length as a #20 Mustad. Of course they won't float as well as a fly dressed on a light wire Mustad hook, so if the fish run small I prefer the lighter hooks.

A Spring Hatch

Spring is a season of promise. The Beaverkill on Easter Sunday was in good condition, the water low and clear, but there was still no trace of spring on the hillsides. Art Lee, Steve Cohen, and I had taken a few good fish on caddis pupae at the head of Wagon tracks before we were chilled out of the water by a sky that threatened snow as much as rain. But our trip back to a warm hearth was stopped by an unusual sight. Cairn's Eddy, the Grand Central Station of the Catskills, stood empty for the first time in my experience. While Art fished the flats above the tail and Steve wisely sat on the bank and chatted with Art's wife, Kris, I crossed the river and fished from the rocky embankment at the head of the pool. Art always chastises me for crawling along that bank, but I was in no mood to dip my lower half in cold water. There were fish rising, as there nearly always are, in the pockets and eddies along the rocks. I thought they were taking midges, but when I stuck my head down near the water to take a look I saw tiny little mayflies drifting on the choppy current. They looked steel gray in the subdued light, but in my hand they proved to be dark olive Baetis. A #20 Floating Nymph, a 6x tippet, and short, downstream presentations along the rocks proved the undoing of several fish that afternoon. None was large by Beaverkill standards, but they were all welcome harbingers of a fresh new season.

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Ken Miyata, a frequent contributor to FFM, lives in Washington, D.C.