A few weeks ago, I was out fishing with two friends when we got into a great blue-winged olive hatch. There were bugs everywhere, the fish were going nuts, and I remember thinking something to the effect of, this will be an easy day.
Four hours later, I hadn’t caught a fish. No one else had, either, but I was having a hard time not taking it personally. I’d switched fly patterns out a half-dozen times, lengthened my leader, and tried every dry-emerger combination I could think of.
The one thing I hadn’t tried was switching the size of my dry fly, because I was convinced I had it dialed in. I finally gave up, though, and swapped my 16 parachute BWO for an 18. On the first cast, I hooked and landed my best fish of the day.
I know how important size is, especially when you’re matching the hatch on a tailwater, like I was. But I’m prone to forgetting the basics at times (as I think we all are) and a refresher is always good. So, in light of that humbling day, I want to share a few tips to correctly size your flies when faced with tough fish.
4 Tips to Properly Size Your Flies
1. Start at 16
During most mayfly hatches where I live and fish, the bugs are usually around a size 16. Of course, weeks after the hatch start, the bugs usually go smaller, but I’ve found a size 16 is a great starting point. Even with a lot of our caddis hatches, a 16 is a good bet.
From there, if you spend a few minutes observing the bugs as they buzz through the air or float on the water, you can get a general idea of whether your size 16 is too big, or too small—a crucial step to properly size your flies.
Last week while out fishing, I got into a March Brown hatch where the bugs were clearly 10s and 12s, based on how puny my size 16 Adams looked in comparison. That size 16 dry fly is an effective reference.
And as with any skill in fly fishing, the more you practice this, the better you’ll become.
2. Refusals are the key
If you find a fish that’s steadily rising, and it either ignores your fly completely, or refuses it at the last second, that tells you something. Most often, what you should take from that situation is that something is off with your presentation. The fly itself is probably fine, but anything from micro-drag to how much leader landed near the fish, could have scared that trout off.
In this scenario (unless I’m being stubborn, like I was a few weeks ago) I’ll fish that fly a few times and try to tweak my presentation before I change much about my fly. If I’m sure the presentation is as great as I can make it, I’ll go ahead and change the fly out to one a size smaller.
If the fish still refuses the fly, even in a smaller size, that tells me I likely have the wrong life cycle stage on (a dun instead of an emerger) or I’m still messing up something with the presentation.
3. Stand out
There is such a thing as a hatch that’s “too good.” When thousands of naturals are on the water all at once, how can you get your fake bug to stand out?
Well, this is when I like to quit trying to match-the-hatch exactly, and go a size up. If all the naturals on the water are a 16, I’ll tie on a 14. One of my favorite tactics is to use a purple variant of that fly, as well. During mayfly hatches, that means I’ll throw a 14 Purple Haze if there’s too many naturals on the water for my Adams to stand out.
I’ve found that just that slight size difference, as well as the contrast of colors, gets a fish’s attention. Sometimes they’ll eat the larger fly, but if you tie on a cripple or emerger behind it, chances are high one of those two fake bugs will fool the fish.
4. Profile matters
Finally, the last tip here is to remember that while size is important (I’d argue the most important when matching the hatch), the profile of your fly matters an awful lot. You can tie up a size 16 parachute Adams that has the silhouette of a 14, or an 18, depending on how short you go with the body, or how thickly you dub it.
Some of the early mayfly hatches where I live feature bugs that are as dainty and delicate as a porcelain doll. As the hatches progress, the bugs seem to be stockier, even if they’re slightly smaller.
Again, the more you practice observing bugs and watching fish, the better you’ll get at noticing these slight differences and the better you’ll size your flies. But it’s all these tiny differences that matter most when you’re faced with a great hatch and picky trout.
Color as well as size can make a difference during a hatch. Many years ago I was in a massive mayfly hatch in Michigan. We hand artificial flies that looked exactly like the mayfly and never caught a one. That night (and I was only 14 at the time) I went back to the cabin and tied a large white wooly moth (chenille body, hackle, and wings). The next night I caught a fish on every cast. That was the night I stopped believing in the importance of matching the hatch. I don’t know for sure, but what I believe is that it generally was shaped like a mayfly, but its white color in late evening made it stand out among the thousands of bugs on the water and that got their attention.