Callibaetis are the most important Western stillwater mayfly of all

There is no insect more important to the Western stillwater angler than the Callibaetis. None.

In some waters, damselflies provide explosive angling for unusually large trout, and on other waters fish wouldn’t survive but for the presence of midges; but taken as a whole, no bug dominates more waters than the Callibaetis mayfly.

Callibaetis (pronounced cal-uh-BAIT-is) are highly tolerant of ecological extremes and will be found in alkaline desert ponds, roadside ditches, sewage treatment plants, and even tidal marshes. It seems however, that the Callibaetis is best suited for those waters that nurture trout, and every Western weedy lake that holds trout will have its population of Callibaetis.

The Callibaetis nymph is available 365 days of the year and it predictably hatches throughout the entire fishing season. The Callibaetis is a flyfisher’s dream, it acts in predictable ways and trout key in on that predictability. The angler who takes the time to understand the ways of the Callibaetis will cross rods with far more trout than he imagined possible.

The Callibaetis belongs to the Baetidae family of mayflies. The Baetidae are extremely important to the flyfisher because many of its members are multi brooded. That is, the nymphs mature exceedingly fast and several generations will emerge within a single season. Compare this to the average mayfly which hatches only once in a brief annual flurry.

The Callibaetis is the most perfectly proportioned of all the mayfly nymphs. The head is slightly narrower than its shoulders and the slender body tapers to three equal length tails that are about as long as the body. Seven pair of heart shaped gills fringe each flank of the abdomen. The sweeping antennae are over twice as long as the head is wide. The only other stillwater nymph that might be confused with the Callibaetis is the Siphlonurus whose antennae are short and stubby by comparison.

The coloration of the Callibaetis is as variable as the waters in which it dwells and the nymphs can change color quickly to match their environment. Because of the tremendous variation in the color of Callibaetis nymphs, I’ve never known trout to be too picky when it came to the coloration of the artificial. The earth tone hues of the pheasant tail nymph seem to be universally accepted by even the most finicky fish.

The nymphs have neither skin nor bones, they have instead, a semi-rigid exoskeleton that must be periodically molted. The typical Callibaetis might undergo a twenty or more such molts throughout the winter.

Early in spring, gasses begin filling the void between the exoskeleton and the body within. As the pressure builds, the exoskeleton starts to swell and the nymph becomes unnaturally buoyant. The exoskeleton stretches thin and radiates a shimmering glow as light reflects from the taught skin and interior gasses. Perhaps to lessen the uncomfortable pressure, the nymph starts crawling upwards. This isn’t happening to a lone individual, but to dozens, hundreds, or perhaps thousands of nymphs at the same time. Up the reeds, and up the rocks, up the stumps, and even up the legs of wading anglers these nymphs migrate toward the sun.

Gas-filled Callibaetis nymph at surface


When these swelling nymphs lose their footing or try to swim, the buoyancy in the trapped gasses lifts them away from familiar surroundings and they desperately swim back down to the protective cover. Soon they will lose footing again and once more be buoyed towards the surface and once again the nymph will struggle back down to cover. To the scuba diver this looks like a beautiful dance as showers of glistening nymphs bob up and down over the weedbeds. To the trout it looks like breakfast.
Every morning, all season long this dance is taking place. The trout grow attuned to the daily rhythm and come to expect the meal that is rightfully theirs. The knowing angler will oblige them.

Get out on the water around nine am. Rig up a floating line with a standard nine foot leader then guestimate the depth of the water you are about to fish. To the end of the leader tie on a 6X tippet one and a half times the depth of the water. In eight feet of water you’ll use a twelve foot tippet. Tie on a pheasant tail nymph of the appropriate size (we’ll get to that in a second). With a series of roll casts work out the line, leader and that hellacious tippet. You will be pleasantly surprised that the tippet isn’t as ghastly as you might have imagined. Lay the line out over the water and be happy as the tippet piles into a big heap.

The nymph will immediately begin to sink, pulling the skinny tippet down with it. Start counting, "one one-thousand, two one-thousand, three one-thousand," etc. As the tippet dives through the film it will create a vee shaped wake with the point of the vee facing the angler. When the vee turns into a circle or dimple, it means the nymph has landed in the weeds and is no longer pulling the leader downward. At this point stop counting and remember the number. For the sake of this article lets pretend that number was eight.

Retrieve the nymph and pull all the weeds off the hook. Cast it out again, watch that vee and start counting. At seven, draw in line with the stripping hand and make one very slow, very long strip until the stripping arm and hand are extended behind you. Trap the line against the cork with rod hand and let the nymph fall. Watch that vee!

By retrieving at seven you stopped the nymph just short of the weeds. The long slow strip does a good job imitating the nymph being buoyed to the surface and the subsequent fall of your pheasant tail mimics the real nymph’s frantic return to cover. This is what the trout expect. When the fish inhales the pheasant tail, the nymph will of course stop sinking and the leader will no longer be making a vee. It will come to a standstill and the water’s surface will simply dimple around the leader. If the fish starts to swim with the nymph (usually they never stop swimming, they just intercept the nymph and keep on cruising) the vee will reappear with the point of the vee pointing the direction of the trout’s travel. Tighten up.

The 6X tippet might seem like a terribly fine connection between you and those lake hogs, but not to worry! Because the tippet is so long it harbors tremendous stretch and will easily control most trout. The skinny tippet is necessary to cut through the water with a minimum of resistance as the nymph falls.

As the morning progresses and the gas continues to build within their exoskeletons, the nymphs acquiesce to nature’s demands and rise to the surface to hatch. At the surface they hold just beneath the film with only the hump of the thorax breaking the meniscus. Within moments the thorax splits and the adult emerges. The mayfly pulls its head and then its legs out of the husk of the exoskeleton. It sprawls the legs out across the water and, levering down against the surface tension, draws the wings and abdomen out of the shuck. Only the tail remains in the husk and then it too pulls free leaving the mayfly to drift across the surface of the lake as it hardens its wings.

Callibaetis Dun - Note the light veins on the dark background.

In the spring the insect is dark sooty gray so that it will quickly absorb the sun’s warmth. As the hatches progress through the season, the Callibaetis are born with increasingly lighter hues to reflect the hot summer sun. In the fall, as temperatures drop, the mayflies once again emerge in the darker colors. The bellies of a Callibaetis are always lighter than the dorsum. No matter the season, all the Callibaetis will have distinctivly light colored veins that contrast with the relatively dark wings giving them a speckled effect, hence the common name the speckled dun.
As the majority of the nymphs drift up from the weeds and converge on the surface, so do the trout. Here the feeding is easy, and at times gluttonous. The fish often disregard the nymphs and duns to feast on the hapless emergers. The emergers can neither swim or fly away and the trout feed at their leisure.

I use two patterns to imitate the emergers: the mayfly cripple, originated by Bob Quigley and the Bivisible Dun. The mayfly cripple hangs at an eighty degree angle in the water so that the marabou on the distal end of the shank dangles in the water like the discarded exoskeleton. A few turns of hackle hold it in the film and a post of elk hair creates the silhouette of the upright wings of the emerging dun. It is a classic, killing pattern, but the Bivisible Dun is even more so.

The shuck of most stillwater mayflies does not dangle below the emerging dun, but is stuck against the tacky underside of the film and extends out from the emerger. The translucent Zelon hangs just below the film and looks amazingly like the slipped shuck of the real bug.

The Bivisible Dun is a sparkle dun pattern with an upright post of white calf body hair stacked against a post of black calf body hair. The beauty of the bivisible post is that the fly can bob into and out of shadows or glare, and one or the other post colors will be easily seen. I use this pattern for fishing just about any mayfly hatch when visibility is compromised. When hatches are dense, the bivisible post acts as an exclamation point telling the angler exactly which fly is his. Even on heavily fished waters with discriminating trout such as the Henrys Fork and Silver Creek, the fish don’t seem to mind the odd looking wings. The Bivisible Dun also makes a great midge pattern because it can be seen even when fished on size 24 and 26 hooks.

A nice thing about fishing emergers is that size isn’t too important. The nymph might be a size twelve and the dun a size fourteen (remember the dun had to fit inside that nymph), but the emerger can be fished all the way to a size ten because it is imitating a part of the nymph as well as part of the dun.

Once the duns leave the water they’ll retire in the lakeside vegetation to hide from the desiccating rays of the sun. The following morning the duns will begin walking around in circles and shudder and shake and act like they ate something awful. The wings spread and quiver then magically the thorax bulges open and a new mayfly quickly and efficiently emerges from the body of its old self. This new incarnation has translucent wings with only a trace of splotching on the leading edge. Like the dun, the hind wings are shriveled useless stubs. The forelegs are spindly, the eyes unnaturally large, and the twin tails are beautifully long and graceful. This is the sexually mature spinner.

Callibaetis spinner. Note the huge eyes - this is a male

The spinner has no mouth parts and the digestive organs have been replaced by reproductive ones. These are winged sex machines that have but one goal in their short lived existence. About mid morning (sometimes in the evening) droves of males rise from the riparian growth and form clouds of insects that fly high into the air and flutter back towards earth. When they reach the level of the riparian canopy (often nothing more than clumps of sagebrush), they burst heavenward once again then repeat their fall.

During the fall the males are releasing pheromones that waft downwind and attract the goggle eyed females. Thus aroused, the females flutter into the bobbing frenzy of males. From your float tube it is easy to discern the males acting like crazed yo-yo’s while the females execute crisp horizontal patterns through the melee. The insects briefly copulate in flight and the males go off to die.

Just about the time the morning hatch is winding to a close, the spinners arrive to lay their eggs. These are the mayflies one most commonly finds crawling all over his body and car during lunch. The female Callibaetis whisk along the surface of the water and dap their abdomens into the film to release showers of fertile eggs. The eggs hatch almost immediately and the cycle begins anew.
Callibaetis spinners can cause tremendous frustration. The angler is doing great during emergence but suddenly the fish no longer want his fly. The trout are still rising, but the pattern that was so successful twenty minutes earlier is ignored. Anticipate the spinner fall. The burnt out females (spent spinners) have no strength left after laying their eggs and wind up on the water with wings flush to the surface. They can be tough for the angler to see, but to trout they are very visible indeed.

As soon as spinners start landing on your arm or the trout begin to refuse your fly, tie on a spinner imitation, but not just any spinner. Most spinner patterns are junk.

The wings of the spinner had to fit inside the exoskeleton of the dun. To fit, they were folded up nice and neat like Geisha fans. When the wings unfolded, they didn’t unfold all the way, but retained their pleats. When the crystal clear, corrugated wings of the spinner lay flush on the water, they trap air in the folds and bends light rays every which way.

From an underwater vantage below and a few degrees to the side of the spinner, the wings are like windows. Through them the sky, the clouds, and the seagulls are clearly seen. This is in sharp contrast to the water on which the spinner is bound which is reflecting the dark bottom of the lake. From directly beneath the spinner, and those pleated wings now glitter like diamonds and spew rainbows like the micro prisms that they are. Compare that to the artificial burnt chicken wing pattern that looked so cool in the fly shop.

The best spinner patterns are barely there; a little fuzz on the hook and a wispy loop of Zelon to suggest the possibility of wings. Add a couple of strands of sparkle organza to add flash and a prism. Not perfect, but usually good enough. The CDC biot spinner also works well because it too has sparkle organza and the fluted CDC feathers trap air like the real spinner wings.

As mentioned earlier, the Callibaetis is multi brooded. It emerges in the spring as a size twelve. About six weeks later, the progeny from the first hatch will emerge but they will be a size fourteen. Six weeks later the next brood will hatch and be a size sixteen and so on until the end of the season when Callibaetis in October are popping off in a minute size twenty. Every six weeks or so will be a major emergence period, but enough bugs are out of synch that Callibaetis hatches can be counted on virtually every day of the season. The nymphs of the season’s last brood having all winter to grow, will emerge the following spring in a succulent size twelve to start the cycle once again. I’ll be there to meet them.

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