They Don’t Have to Eat It to Learn to Reject It

by | Jun 8, 2021 | 21 comments

There are many myths in fly fishing. Common confusion and conjecture comes from a sport where only a small fraction of anglers get much time on the water to really learn things first hand. So almost no one gathers enough data to find their own answers. And those anglers who do are a secretive bunch.

But fly fishers desperately want the answers: what fly, what line, what tippet, what tactic, how deep, how fast, etc. And yet, there are so many variables, that the theories and answers expand exponentially with each new question. It’s enough to make a person walk away from fishing altogether. But we don’t. No, the mystery is what draws us in and holds us here. The open questions and myriad answers of conditional certainty are accepted like a worn-in pair of waders. The whole thing just fits us. Because none of this is easy, and we wouldn’t want it any other way.

I do find myself in a position of the constant contrarian. Not by want or habit, but because I’ve been fortunate to spend a life on the water. I’ve fished endless seasons focused on trout habits and angler errors (my own). I’m a severe critic of my failures, and I don’t stay satisfied with success for long. So, I feel like I’ve spent enough hours out there to form my own opinions based on experience. Add in the group of anglers that I fish with and share ideas with, and I have a lot of first hand information to bundle together and learn from.

However, many of the popular beliefs (myths) in this sport are based on nothing more than the repetition of an idea that somehow takes hold and spreads.

— The biggest trout in the river become nocturnal feeders exclusively. (No they don’t.)

— Winter fishing is best in the midday sun. (No it isn’t.)

— Trout over eighteen inches become predators that eat only small fish. (Nope.)

— Trout take mouse patterns at night. (Not with much confidence, they don’t.)

— Most of the trout in this river love chasing streamers. (Please take me to those fish.)

— You can only catch trout in this river with #20 flies or smaller. (Time and again we’ve proven that one wrong.)

See what I mean? The constant contrarian. And I don’t mean to be. I just seem to form opinions and preferences that don’t often jive with the common wisdom (again, myth). Let me acknowledge with candor that I could be wrong about a lot of this, and I’m likely wrong about some of it.

But here’s one that I’m extra confident in . . .

Trout Learn to Reject a Fly Without Ever Eating It

You’ve probably heard this a lot: “These trout have been caught on that fly before, so they won’t take it.”

Or this: “Once trout are caught on a fly a few times, they learn that it’s a fake.

Sure that makes some sense. I’ve seen it. And I recently wrote about the phenomenon with the Squirmy article.

But trout don’t have to be caught on a fly to learn that it isn’t real. They don’t need to take it in their mouth and eject it. In fact, just seeing one bad drift after another is enough to put a trout off of a particular pattern.

We witness this on a small scale all the time. Take the dry fly game, where everything is easily seen up top: success, failure, hits, eats and refusals. If you’re set up in a piece of flat water over a couple of rising trout, maybe they take a look at your fly the first time through and refuse it. If you’re really lucky, they might give it another look, but by the fifth or sixth drift, your odds of catching that trout have gone way down. You’ve seen it. You know what I mean. But that fish never ate the fly, right? He just saw it dragging. Or he inspected it close enough to see it as a fake. Either way, he rejected it.

Trout learn to refuse a fly without ever being caught on the pattern. If they see enough pink-beaded nymphs from a multitude of anglers, then they surely see it dragging through the currents at every angle imaginable. And they eventually associate that fly, that look, with something to be avoided.

Do trout reject a fly even more after they are caught on it? I don’t know about that one. But it seems that they do not. No, I think it’s more about repetition. To me it’s the frequency at which they’ve seen bad drifts on a fly. That’s what adds up in their tiny brain to somehow influence a refusal.

Photo by Austin Dando

As always, I welcome your thoughts in the comments section below.

Fish hard, friends.


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Domenick Swentosky


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Domenick Swentosky

Central Pennsylvania

Hi. I’m a father of two young boys, a husband, author, fly fishing guide and a musician. I fish for wild brown trout in the cool limestone waters of Central Pennsylvania year round. This is my home, and I love it. Friends. Family. And the river.

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  1. This is so true. On my streams if I get a last minute refusal on a particular dry pattern due to drag, the same fish will never rise again to that same pattern, even if subsequent drifts are perfect/drag free. This is in freestones with limited food with fish that are not picky at all. Sometimes if I rest the fish for 5-10 min and change the dry pattern, or add a trailing tiny dropper, they’ll eat, but they’ll never eat the original pattern.

      • I’m not a great fly fisherman, but I do catch trout. Fishing the spring creeks in Montana is like going to trout fishing grad school. Difficult. But, with persistence and observation you can catch a specific trout using the same fly after multiple casts by casting about 6″ in front of the fish and timing it’s rise pattern. If I were better I might catch it on a second cast instead of the tenth cast….. But, the same fly and patience usually wins a hook up.

        • Agreed. The spring creeks are the same here. Please note, in the article, I’m speaking of long term and groups of fish. I only used the short term, one fish, dry fly as an example of something that happens a lot too. Because in most cases, once a wild trout refuses your fly, your done with that trout.

  2. I agree. In fact, a prominent US Team competition fly guy I know has made the point that although the patterns are important, even the ‘wrong’ fly has a better chance with good presentation than the right fly presented badly. I subscribe to this and worry far more about improving my drifts and presentation than I do trying to dial in the perfect fly

  3. The effect you describe sounds like habituation. If it is, then substituting a different fly would “reset the clock” so-to-speak. Then success on the first presentation of the novel stimulus might be predicted. But repeated presentation of the novel fly might result in habituation. Changing the fly might not work because several factors that promoted the initial habituation remain, for example: the position of the trout, and the surrounding currents , the angler and their presentation style, stimulus equivalence i.e. the assumption that the first and second fly are equally attractive to the fish. This last requirement could be very difficult, but not impossible, to fulfil

    • Good call. That’s a short term perspective too. Mostly, when I think of this, I think about long term, repeated exposure to a fly.


    • Habitation involves a diminished response to an inconsequential stimulus. Being hooked repeatedly by a squirmy worm and learning to avoid it would be properly classified as operant conditioning; think Pavlov’s dog if he got beat every time a bell was rung. After a while he would cower or run away. This is also very common in bass fishing where after a year or two, the hot lure is no longer hot. However, the more natural and subtle the lure or fly is, the less prone it is to operate conditioning. Trout continue to be caught year after year after year on sulfur duns and pheasant tail nymphs yet hot pink squirmy worms, not so much.

      Introducing the variable of drag is a different story. If the drag is severe it could simply put them on high alert. The mood change may be as big a factor as the pattern.

    • Habitation is also a feeding technique used by many predators. The Blue Heron standing motionless poses no threat to prey fish and eventually their response (increased alertness) diminishes and they relax even with this lightning quick predator standing just a stab away. Anglers, as predators should learn a lesson: wade like a heron -and wait like a heron!

  4. Too many variables in play. E Persistence and patience amust. Go down a tippet size and fly size or shift to a cripple

  5. Fished a streamer yesterday, caught 10, 8 of them between 16-20”, all wild browns.
    Rain overnight, streamer conditions even better today. same spot with same streamer, no fish, no hits, no follows. I was full of confidence at the beginning! Not so much when done.

  6. I’ll be the first to request a feature length article on commonly held fly fishing beliefs and your scientific observations about them, true and false. A lot of the people promulgating these beliefs seem to be better writers than fishermen, which is fine, but I sure appreciate your writing which is much more signal than noise.

  7. I know it’s completely anecdotal evidence, but I do have an experience that suggests trout may not become ‘fly shy’ after getting caught. While living in NY on the banks of the Mohawk River, I wasn’t having any luck as dusk set in on a Sunday night in the summer. Switching to a #14 Light Cahill dry (so I could see the fly), I happened to catch a small trout behind a rock. The trout fought hard but I finally brought his 7” body to my hand then promptly released him. Next Sunday, same slow fishing in the heat & humidity. I decided to go with the same fly and cast to the same rock. Bingo! After a few runs and head shakes, the fish gave in and I brought his 7” body to my hand. I noted similar markings to last week’s fish and promptly let him go. I wouldn’t have thought anything of this except the next week the same thing happened. Same slow fishing with the same fly and the same place. This time, the trout shook it’s head once and gave up. Once in my hand, the colorful 7” looked amazingly similar. I wasn’t able to go back the next week to try again.

    I know there are so many variable that suggest this was a different fish. However, it was the only fish I caught each night. The fish gave up much faster each fight (although water temps would have some effect there too). The fish was at the same location, and it did take the same dry fly. Always made me wonder if it was the same trout and, if so, it would suggest trout don’t become ‘fly shy’.

  8. Hi Dom,

    Great post. I would go a step farther into contrarianism here and suggest that trout probably don’t learn to recognize specific flies or fly patterns at all, but might instead learn to associate certain features they don’t otherwise see (like pink beadheads) with other unnatural observations (like drag) that signal “not food.”

    There’s a lot of variation in how a fly looks to a fish on each cast, especially a dry with the different ways it can sit in the surface film, but it’s even true for a nymph rolling by at different angles (head-on, side view, top, bottom, etc) through varying lighting against varying backdrops.

    There’s even greater variation in how real food appears to the fish; just multiply all those visual factors by all the different types of food and ways they move. And there’s still more variety in the natural, non-food debris fish encounter, which greatly outnumber prey (by a factor of tens to hundreds, depending on the size of the fish). Most fish are sampling these debris and spitting them out (or rejecting them visually) more often than they’re taking real food, except probably when feeding selectively on hatches (which makes it easier to reject almost all debris, at the cost of rejecting other kinds of prey).

    I think ultimately fish are faced such a wide variety of visual images of potential prey, all coming at them in motion and requiring very quick decisions, that there’s very little opportunity to recognize an entire object as something they’ve seen in the past, except for certain real prey they’ve seen many times from every angle. Even then, given the variety of possible images, it’s likely they’re just keying on a few features. We just have to figure out how to catch their attention, check those boxes, and not raise any red flags with whatever gaudy additions we used to catch their attention.

    When it comes to fairly realistic imitative patterns, I would be surprised if a trout ever refuses a fly because it thinks it’s a fly. Most likely the fly just isn’t checking all the right “food” boxes.

    • Hi Jason.

      Love your website, by the way.

      “. . . trout ight instead learn to associate certain features they don’t otherwise see (like pink beadheads) with other unnatural observations (like drag) that signal “not food.”

      I agree completely. And that is the essence of the article above.


  9. As a fly fisher… and a fan of great literature regarding the same – I have consumed all of John Gierach’s books – some several times… and while doing so – I have been in search of authors that can fulfill that quest. Up until today – I had not found that …. Now I have . Well written – well read.


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Domenick Swentosky

Central Pennsylvania

Hi. I’m a father of two young boys, a husband, author, fly fishing guide and a musician. I fish for wild brown trout in the cool limestone waters of Central Pennsylvania year round. This is my home, and I love it. Friends. Family. And the river.

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