Part 1: Trout and the casualty dry-fly
An imitation of a perfect adult dun is not always the most effective, says Don Stazicker, who has found that trout favour dry-flies suggesting vulnerability
YOU’RE WATCHING a wildlife documentary. A herd of wildebeest is thundering across the Serengeti when suddenly they’re ambushed by a pride of lions. The leading lion rushes in and attacks the big alpha male at the head of the herd.
Well, that just doesn't happen; there’s too much chance of failure, too much risk of injury, and crucially, too much expenditure of energy.
Which wildebeest, then, will the lions target? Sadly, it’s the poor little straggler limping along at the back of the herd. It will be easy to catch, pose no risk, and require minimal effort to bring down.
Predators are successful when they load the odds in their favour. This can be described as “efficient foraging” — maximising calorie intake while minimising energy expenditure. In practice, it means tackling the vulnerable instead of the healthy. It means targeting those that cannot get away.
Most of us know that well-used and tatty flies work, so why don’t we tie them like that in the first place?
Trout are no different and will, when given a choice between a fully-formed dun and a vulnerable emerger, generally choose the easy meal. The fish that forage efficiently thrive and produce offspring, while those that don’t starve and lose their DNA from the gene pool. There is no conscious thought involved in this process. It’s the result of countless generations of fish subjected to natural selection that has determined what they feed on and how they feed on it.
So, why have we been tying flies that don’t represent the preferred prey of trout? What we’ve been doing is tying the very flies that, given a choice, they prefer not to eat.
It’s not that we haven’t had plenty of clues. Who hasn’t had a successful fly that remained effective, or became more effective, as it got chewed by subsequent fish? Most of us know that well-used and tatty flies work, so why don’t we tie them like that in the first place?
Perfect duns
Instead, we commonly go down the route of creating the “perfect fly”. We expect our dry-flies to land upright and float “fully cocked”, standing proud of the surface on the steely fibres of the gorgeous genetic hackle with which we’ve so carefully constructed them, giving us the “perfect dun”. We would be delighted if our flies achieved the “perfect float-line” with the hook supported by a stiff tail and hackle and just kissing the surface. It’s a shame that they always fail to do so.
A heavily hackled traditional dry-fly that does not float as it was designed to. Its tail, hackle and hook beneath the surface do a poor job of imitating a perfect dun.
Viewed from underwater, the tail, hackle and hook of this traditional dry-fly are clearly visible to the fish, suggesting a vulnerable emerger or failed hatcher rather than a perfect dun.
If your dry-fly didn’t float fully cocked, with its divided quill wings pointing skywards, you weren’t considered to be fishing in a gentlemanly manner
In Frederic Halford’s time, if your dry-fly didn’t float fully cocked, with its divided quill wings pointing skywards, you weren’t considered to be fishing in a gentlemanly manner.
There is very little evidence to show that anglers of that period troubled to look closely at their dry-flies on the water. If they had, they would have realised that the perfect float-line is virtually impossible to achieve.
Instead of these traditional flies riding high, they have portions of the hook, tail and hackle sticking down beneath the surface and look much more like emergers or failed hatchers than perfect duns, even when densely hackled. Because they failed to replicate the perfect dun, these traditional dry-flies worked reasonably well. Bizarrely, if they had worked as intended, they would have been far less effective.
This doesn’t mean trout won't eat perfect duns, both natural and artificial — they certainly do. However, when presented with a choice, they typically opt for the easy meal, such as an emerger or a failed hatcher. In a decade of filming, I’ve never seen trout ignoring the vulnerable stages and targeting perfect duns, but I’ve frequently filmed them taking vulnerable flies and ignoring perfect duns.
But what is this perfect dun that we are trying to imitate? An adult fly that has emerged with complete success, erected its wings and is just about to take off; a fly that is likely to escape before being eaten; a fly that a trout will ignore if an easier meal is available.
I’ve never seen trout ignoring the vulnerable stages and targeting perfect duns
We need to stop trying to make precise imitations of perfectly emerged natural flies and start designing patterns that suggest vulnerability as the trout sees it. The best part of this is that it's much easier to tie scruffy, battered, vulnerable-looking flies than those immaculate specimens that win fly-tying competitions.
Not that your flies shouldn’t be well tied, durable and capable of being accurately reproduced. But you need to stop tying flies that may well take off before the trout get to eat them.
If vulnerable flies are available in sufficient numbers, the trout may become selective to them. To be successful, you will need to imitate not only the insect, but the stage of that insect that the fish are selecting.
Emergers
When the adult fly is still partly within the nymphal shuck, the trout sees a food item that is significantly larger than either the shuck or the adult alone, and, crucially, something that cannot suddenly fly away. The large size and the shuck hanging beneath the surface, possibly moving as the fly struggles to escape, provide clues to the trout that this will be an easy meal.
An emerging mayfly: the wings of successful emergers do not contact the water’s surface.
If emergence occurs slowly, trout will take the emerging insects and an emerger pattern will be effective. Some insects emerge extremely quickly. Under suitable conditions, Ephemera danica mayflies can breach the surface, emerge and fly away in under three seconds. In this instance, the classic emerger pattern with its shuck and partially exposed wings represents a stage that may only be fleetingly available to the fish.
Failed hatchers
From the moment an insect reaches the surface until it is successfully free from its nymphal shuck, emergence can fail. If this occurs, the adult fly becomes permanently trapped in the shuck with a portion of its body protruding and becomes a failed hatcher — an emerger frozen in time.
A mayfly that has failed to hatch, still in contact with its shuck after failing to free one wing.
This may happen because wings or body parts cannot pull free from the shuck or because the fly drowns during emergence. These failed hatchers are available to the trout for a much longer period than emergers, and it is likely that many of our fly patterns that were designed as emergers are taken as failed hatchers. If this is so, why do we need new patterns — why not keep on using emergers? The answer is that it’s possible to design more effective flies if we understand both the similarities and the differences between the two.
Emergers and failed hatchers have something in common: the shuck is submerged and consequently directly visible to the fish from a long distance — a much greater distance than a fully emerged fly standing high on the surface.
One distinct contrast is that the failed hatcher frequently has a wing, or wings, in contact with the water’s surface or submerged beneath it, whereas with the emerger, the wings never contact the surface. Another common difference is that failed hatchers frequently lie on their sides, something that successful emergers never do.
Casualty duns
Even if the fly has successfully emerged and is standing on the surface, completely free from its shuck, things can still go horribly wrong.
This mayfly casualty dun, having successfully freed itself from the shuck, has caught its wings in the surface film. Its struggle signals vulnerability to the trout.
A blue-winged olive (Serratella ignata) casualty dun. This species has a relatively small body and large wings. While warming its flight muscles, the dun flaps its wings vigorously and becomes caught in the surface.
An adult caddis casualty: all orders of aquatic insects can become vulnerable flies, as can terrestrials that find themselves on the water.
Following emergence and before flight, many aquatic insects flap their wings. Not to dry them; they were never wet. They are warming up their flight muscles enough to fly away. This takes longer on colder days, when there will be prolonged wing flapping and the flies will drift for longer before flying off.
During this time, the fly may overbalance and get one or both wings stuck in the surface. Or the wind may blow the fly over with the same result.
If the wings get stuck, they are often stuck for good. This occurs frequently in areas such as backwaters where scum accumulates and makes the water’s surface “sticky”.
The flies that have successfully emerged, freed themselves from their shucks, and have then come to grief, are casualty duns. They appear different to emergers and failed hatchers because there are no shucks present, and they differ from perfect duns in that they are not standing clear of the water but are trapped in the surface.
A trout feeding on casualty duns
Don Stazicker and Peter Hayes (narrator) recorded this video on Nelson’s Spring Creek, which flows into the Yellowstone River south of Livingston, Montana.
On this hot, bright day, a big brown trout was sheltering beneath a weedbed.
The current gathered casualty duns and the trout fed on them, disregarding all of the fully emerged duns that drifted by.
DON STAZICKER
Many types of casualties were taken, but all had at least one wing in contact with the water, distinguishing them from the perfectly formed duns supported by their legs on the surface. Most of the perfect duns flew away, leaving behind the vulnerable flies unable to take flight. These were duly mopped up.
When the footage is slowed, we can see events clearly. However, when shown in real time, the human eye cannot capture the fine detail of what is actually happening.
Signalling vulnerability
A chaotic appearance, usually with portions of the wings, body and possibly shuck trapped in or submerged beneath the surface, is a sign of helplessness to trout. It’s a stark contrast to the perfect dun, whose feet and possibly abdomen cause tiny imprints on the surface, and whose wings are completely clear of the water.
Vulnerable flies have no standard appearance. Anticipating their form is like wondering what your car will look like after an accident — it’s completely unpredictable and depends on many factors.
Wings, legs and tails may be present, distorted, partially or entirely missing, but there’s always a thorax and abdomen
However, one thing is always there: the body. Wings, legs and tails may be present, distorted, partially or entirely missing, but there’s always a thorax and abdomen. When mayflies die, their abdominal muscles contract, causing the abdomen, lying in the surface, to assume a distinct curve. Patterns that imitate this curve have proved highly successful. They are best tied on curved hooks to create a fly where the hook lies flat in the surface. From beneath, the curved hook imitates the curved body of the dead insect.
Three vulnerable flies: a BWO Emerger with a Zelon shuck and CDC emergent wings (top); a BWO Casualty Dun tied on a curved hook to lie flat with its wings stuck in the surface (middle); and a BWO Failed Hatcher imitating a drowned fly, partially out of the shuck and with its wings trapped in the surface (bottom).
PHOTOGRAPHY: DON STAZICKER
ABOUT THE AUTHOR
Don Stazicker
Don Stazicker is the president of Cressbrook and Litton Flyfishers in Derbyshire, England, and co-author — with Peter Hayes — of The Flies that Trout Prefer. Why they work and how to tie and fish them.
