Trout Fly Choice – Part One

In the first of two parts, Philip wrestles with an inexact science.

I’ve helped a lot of inexperienced anglers with their flyfishing for trout; a few thousand so far. And a common issue for just about all of them – not to mention a number of their more experienced brethren – is fly selection. Speaking of which, just last season, one of my guests with several years of flyfishing behind him, got quite angry with me for not having written a nice tidy book about what trout flies to use and when: i.e., in situation 3, use fly C, and so on. When I explained that, because of all the variables, I couldn’t in all conscience do that for every fishing destination (and effectively for every day of the season) he just got madder!

I get it; well… sort of. But flyfishing should never be something that makes you angry. Perplexed, confused or challenged? Absolutely. Angry? Find another sport.

Fly selection can still be an issue for me personally sometimes. I had an experience at Tullaroop Reservoir in late winter, where I spent an hour on a steadily-feeding trout which I simply could not fool. I put perhaps a dozen different flies on its nose or almost – static, landing like a feather, plopped down, twitched or stripped. No response. In the end, I surrendered and handed the fish over to my mate. He couldn’t catch it either.

So, when I write about trout fly selection, it’s not from the perspective of a guru who knows it all. However, perhaps I can offer some ideas about the process.

Hmmm, which one?


This is a good one to get out of the way early. As is the case with humans, and just about every other lifeform, there are trout which behave differently to most others. Aggression versus caution, choice of spawning habitat (home riffle versus a 50 kilometre journey); even ability to ‘specialise’ in certain prey. At Newlyn Reservoir, I’ve caught a couple of good brown trout with soft bellies and smelt spewing from their mouths, then 30 minutes later, another with a belly crunchy with snails and not a smelt to be seen. This all makes sense from a species survival viewpoint: a homogenous population is very exposed to a single natural disaster.

Where it gets really interesting, is when you get trout behaviour at the extreme ends of the statistical bell curve. It may be for a moment, or it may be a regular thing, but the point is, these trout are outliers. These are the fish that eat your huge orange indicator while nymphing a stream. Do you change to a giant, pure orange dry fly with a hook in it? I’ve tried – quite a few times – but hardly ever has it worked, and it has certainly never out-fished the conventional nymphs below.

Two cast before this Tassie river beauty took a brown nymph, a much smaller trout slashed at the pink indicator above – the only time that happened all day. Just as well I persisted with the nymph instead of changing to a purely pink dry fly!

So, as a flyfisher, you have to decide whether you want to target the vast majority of trout in the middle of the bell curve, or the handful at either end. Yes, it is possible to catch Penstock trout feeding flat out on mayfly duns with a stripped Magoo, but that’s not the best way to catch most of them. To put it another way, catching a single dun feeder on a Magoo, is not proof it’s the best fly choice. It’s only proof that a trout was prepared to eat it. Persisting with that fly and that method may or may not catch another fish, but the odds are against it.

I could possibly catch any trout under any circumstance by persisting with one fly I had faith in… eventually, although that might take hours, days or months! However, I would argue that if you want the best trout-catching outcome, you can’t accept an outlier as any sort of proof of success. 

Some key points

With outliers dealt with, here are some important fly choice points:

  1. Trout usually choose to eat flies (or not) for sound reasons, even if those reasons might sometimes seem irrational to us. Any fish that has survived several months in the wild has learnt to feed wisely – those that haven’t are dead. For example, a common frustration for inexperienced flyfishers, is trout knocking back the supposedly decent meal of a large fly, in favour of something tiny. But the fish will be doing this for reasons other than to annoy anglers – more about this shortly.
  1. What you do with a fly is at least as important as the fly itself. A fly pattern that’s a perfect fit for a given situation still won’t work unless:
  • You place it where the trout can find it.
  • You put it there without scaring the fish.
  • It behaves in a realistic way; e.g., swims like a baitfish, drifts like a beetle, or hugs the bottom of a rapid like a real nymph. In other words, it behaves as trout expect their prey to behave, whatever that behaviour may be. These presentation components are crucial, and you can’t blame the trout for refusing or ignoring a fly if these steps aren’t executed well. Watch what the naturals do and try to make your fly do the same.
  1. Trout will sometimes eat a fly out of pure aggression or curiosity, rather than because they recognise it as potential food. However, in the same way I recommend against relying on or targeting outliers, I suggest you mostly use a ‘food’ fly to get a trout to eat.
  1. It is very rare (although not unheard of) for a single precise pattern to have an unbeatable advantage over every other fly ever made. Near enough is usually enough; good news if you don’t have a thousand different flies at your fingertips. More about this point shortly too.

    Trout ‘smutting’ on size 18 caenids aren’t doing so to annoy us – although it might feel like it sometimes!

Selective feeding versus opportunistic feeding

Trout spend a lot of their lives feeding opportunistically – eating anything they find that could conceivably be food. As with all predators, from lions to eagles, trout need to take their opportunities when they can. A minnow here, an ant there… The sheer variety of food a trout will eat is extraordinary. Everything from zooplankton to mice can be on the menu.

But sometimes, trout will feed selectively: targeting a particular food to the exclusion of all else. For this picky behaviour to make sense, there needs to be an awful lot of that food type. So, selective feeding is more common in fertile environments like weedy lakes, and less common on, say, a typical rainforest stream with a steep gradient. But it can happen anywhere.

I imagine it works like this: a trout is feeding away on a bit of this and a bit of that, when a particular kind of food begins to appear in ever-increasing abundance. If that food is relatively easy to catch and relatively nutritious (let’s say chironomid/ midge), at a certain point, the trout becomes single-minded about it. Like a toddler following a trail of Smarties, it is soon very difficult to distract. Even the proverbial Mars Bar is ignored. And it won’t be long before every trout joins in (except an outlier or two).

Now, this fairly abrupt transition to singling out one type of food can be heaven for the angler… but potentially hell. All those rises/ disturbances the trout are now making, are occurring precisely because there is so much real food. So, not only do you need the right fly, but you also need to put it right in front of a trout. Such is the blizzard of midge, a fish doesn’t have to detour: the little insects are lined up in front of it.

Emergers (like this emerging chironomid) only exist in that state for a few seconds, yet they are an incredibly vulnerable, and therefore appealing, stage for the trout – and often worth copying with flies.

At its worst (best?) trout can even home in on one stage of the event. In the case of many insects (chironomid included) that may be the sub adult swimming to the surface, or the ‘emerger’ pulling off its wet suit, so to speak. Or it may even be the fully-formed adult which attracts the most attention. Whether it’s one stage or all of them, you can rest assured that, no matter how frustrating or illogical it may appear to us flyfishers, there will be a good reason for the behaviour down in trout land.

I’m not writing all this to intimidate or confuse, only to demonstrate the impact selective feeding can potentially have on fly choice.

And if this is all sounding a bit hard, there are a couple of pieces of good news. In Australia, selective feeding makes up the minority of a trout’s eating time. And even when it does happen, it can often be a lot simpler than a chironomid hatch – like during a big fall of beetles or grasshoppers, when plopping down a nice chunky matching dry fly, roughly in the path of the fish, will do the job perfectly.

Another positive about selective feeding is, by virtue of the sheer quantity of food required to cause it, with careful observation, more often than not you can soon see what’s creating all the fuss.

Fly choice for opportunistic trout

To reinforce the point, in Australia, trout feeding opportunistically are the ones you are most likely to encounter hour to hour and day to day. There are two ways to tackle these opportunists:

  1. Fish a fly which represents something your target trout are likely to be encountering regularly, even if it’s not the only thing they’re eating.
  2. Or, use a generalist fly; one which isn’t intended as a copy of a single thing, but which is sufficiently ‘buggy’ and attractive to suggest food.

Stimulators are a rightly popular ‘generalist’ dry fly, especially on fast-flowing streams. The white wing aids visibility – a handy consideration in broken water.

While the line between these two categories of fly can blur (e.g., you can fish a Woolly Bugger specifically to suggest a Lake Eucumbene yabby, or simply as a nice bug-like all-rounder) this approach is a good starting point when choosing a fly to fish with confidence.

Classic ‘generalist’ flies for opportunistic trout might include Woolly Buggers and variants, Magoos and variants, Yetis, Royal Wulffs and Stimulators. Meanwhile, many stick caddis patterns, BMS baitfish patterns, flashback nymphs, Pheasant Tail Nymphs and the Tom Jones, are examples of flies that were originally designed as quite specific imitations, but which many trout in many waters would recognise as food sufficiently for them to be effective on opportunistic fish much of the time.

Fly choice for selective trout

Much of flyfishing’s mystique has evolved around trout feeding selectively – and the need to find the fly or flies needed to bring these fish undone. If the trout are eating those big beetles or hoppers, it’s quite easy and unambiguous to observe, and then to dip into your fly box, tie on something similar, and make the right presentation. And if the quantity of food isn’t ridiculous, you may even find the fish will move a foot or two to eat your imitation.

But now for some tough love: imitative patterns often need to be… well, imitative – and presented with precision. I could tell you numerous stories of seemingly perfect imitations failing because they were out by a hook size. For example, one afternoon on New Zealand’s Motueka River, Felix and I fished size 14 Parachute Adams to dozens of rising fish during a massive dun hatch. The Parachute Adams seemed a good match in shape and colour to the real duns, yet we fished for not a single take.

Eventually, a closer look at the naturals revealed that perhaps the size 14 flies were a fraction too large. A change to a size 16 brought a rise from every fish – provided it was placed where the trout could see it, and it drifted like the real mayfly.

A real mayfly spinner, and passable imitation, at Newlyn Reservoir recently. The abundant red spinners, many of which were actually on the water like this one, were being actively targeted by the trout.

One quite credible theory is that selective trout soon form a precise search image. Objects which don’t match the size, shape, colour or behaviour of the new and abundant food, aren’t merely refused, they’re simply not noticed. Perhaps it’s a similar situation when we’re trying to cross a busy road. We might ‘see’ the other people, or dogs, or birds, or parked cars, but we don’t notice them – only the moving cars we’re trying to avoid.

How high or low an imitative fly floats might seem a ridiculously obsessive detail, but to the trout, plenty of fly ‘hull’ breaking the surface film and appearing in their world, can suggest an emerging insect, or vulnerability, or both. Conversely, a fly sitting on its well-hackled tippy-toes, might suggest an airborne mayfly spinner or damselfly; enough at least to fool some of the trout taking these insects in flight.

The quest for imitative detail can go too far though. It’s unlikely, for example, that trout count the number of legs on an ant before eating it. It makes sense that, in the quest to consume as much as possible, trout probably don’t take the time to look for minute detail. As per above, the right size, shape, colour and behaviour – including position and movement on or under the water – is enough to fool them.

And yes, the spinner imitation proved a good enough fly option for three decent trout feeding selectively on the real thing… but it still took several fast and accurate ‘intercept’ presentations to get a rise.

It’s worth noting that, for many years, anglers have suggested you can improve this prey recognition ‘shorthand’ by exaggerating a key feature. One classic example is an overly large and dark wing-case on a mayfly nymph pattern – a prominent feature on preemergent nymphs, and arguably something which trout nymphing during a hatch would home in on.

It could also be colour, such as an exaggerated splash of bloodworm red on the thorax of a midge pupae, or maybe an oversized tuft of bright white fibres for gills. As another example, I often make the protruding grub of my stick caddis a ‘hotter’ yellow or green than the real thing. If you’re hunting trout that are picking out the goodies from all the rest, it’s sensible to help their decision-making… except the challenge is not to overdo it to the point where your fly falls outside the parameters of the bug you’re trying to copy.

Exaggerating the prominent wing-case on mature mayfly nymphs is recognised as a way of increasing the ‘pulling power’ of imitations – and looking at this preemergent Colorburiscoides nymph, it’s easy to see why.

If you’re still struggling with the thought of trout finding your fly in the crowd, a similar strategy is to use a fly which is basically an imitation, but with a random dash of colour or flash to help get it noticed. While not strictly natural, a fleck of silver on a mayfly nymph, or a few wraps of orange thread at the head of a baitfish fly, may help your offering stand out, without overwhelming its imitative features.

More to come on trout fly choice in part two in our summer issue.