In Defence of Smaller Flies

One mistake that many fly anglers make when fishing productive trout streams is using flies that are way too big. If there is nothing actively emerging (and sometimes even if there is) the tendency is to work a searching pattern through likely holding water in hopes of a take. To most anglers a searching pattern means something large and buggy looking – the theory being that a larger, more visible fly will be more likely to generate some interest from the fish (especially if the water is stained from runoff). And if nothing else, the thinking is that the fly is at least more visible (or attractive) to the angler. This line of thinking may seem to make sense, and there is no denying that large searching type patterns produce their fair share of fish (especially if fish are feeding opportunistically), but this way of reasoning is based on a few flawed assumptions.

The first assumption is that in murky water, fish have trouble seeing a small fly, and somehow need to be helped out a little. Make no mistake, trout have excellent eyesight – they have evolved over millions of years to maximize caloric intake in all but the worst of water conditions. In addition, much of what a trout eats is small in comparison to what anglers typically offer them. Spotting and intercepting tiny nymphs in the tumbling current is what trout do for a living, day after day for their entire lives, and they do it very well. Regardless of the conditions, whether your offering is size 8 or size 18, the fish knows your fly is there.

The second assumption is that a larger fly will be more attractive to the trout because it offers more calories for the same amount of effort. This is a part of what is known as optimal foraging theory (OFT); and it is a valid assumption, but it does not take into account some of the more intricate aspects of OFT and trout feeding behavior.  If you are a trout and you have been feeding on tiny Baetis nymphs or Midge pupa for the past few days, you recognize them as food and you know exactly what to expect. The result of grabbing one out of the current is predictable and rewarding (i.e. food); and there is little or no hesitation. Compare this with something larger and unexpected. You are not sure about it – it looks like it could be edible. You could sample it at the risk of wasting valuable energy; or worse, another unpleasant encounter with an angler, or just let it pass on by. There is hesitation. Maybe even apprehension (have you ever watched how a trout reacts when a suspicious fly drifts past – that fin twitching, nervous behavior). Maybe the fish was hooked several days ago and is reluctant to take the risk. Which fly do you think will result in more takes?

I am of course ascribing some human attributes (i.e. thinking) to an animal that relies primarily on instinctive and learned behavior, but the end result is the same.

The final assumption is that most of the bugs that trout eat are as large as the impressive stonefly nymphs and caddisfly larvae that one sees wriggling in screened kick net samples. The larger organisms certainly stand out more than everything else (or at least are more active). But if you were to count up all of the different types of bugs in a kick net sample you would find that most of the time it is the tiny, unassuming mayflies and chironomids that far outnumber their more showy brethren (remember that many kick net samples are usually taken on a shallow riffle – prime habitat for stoneflies. How much of the river is actually riffle?). Big bugs are great if you can get them, but if most of the drift contains smaller organisms, then that is what you will be eating most of the time. Even if you are a bigger fish, your behavior is molded by what is most readily available (remember my example of the bear tearing open the log to get at a mouthful of insect larva - see the Introduction to Bug Bits).

There is no doubt that anglers will continue to catch their share of trout on larger searching type patterns. And these patterns do have their place even in my fly box. But I find that smaller flies that more closely represent what is actually present and active in the water consistently result in more hookups. Further, bigger fish that got that way by being a little more suspicious than the rest are far more receptive when confronted with a fly that does not look so out of place. Next time you are on your favorite trout stream try downsizing to a more natural pattern – you may find that this is just what is needed to fool the big one that has eluded you so far.