Mike Pawlawski
January 13, 2023

What is the best fly for Trout?

When it comes to fly selection there are as many opinions as there are flies in your local fly shop bins. Trout flies come in a variety of flavors. Size, shape, style, color, and dressing all change from fly to fly. Anglers have been tying flies for hundreds of years which means there is an amazing variety of fly patterns to choose from. So when you ask which fly is best it's a very subjective question.

Trout flies are designed to mimic the naturally occurring food sources that trout feed on every day. Essentially aquatic insects, smaller fish and other aquatic life such as cress bugs and even crawdads. If it doesn't look natural they aren't going to eat it. That being the case, the best possible trout fly is the fly that most closely matches the food source that trout are focused on at the moment. Here's the trick, many times, it switches throughout the day.

I'm gonna explain the keys to selecting a fly when you're fly fishing for trout, and why size really does matter in fishing flies.

The beauty of fly tying lies in the fact that a skilled tyer can tie the patterns that give him the most confidence on the stream. Fishing fly sizes vary greatly from pattern to pattern.

Understanding Fly Sizes

The size of a fly directly affects the fly's ability to mimic the natural insects that trout feed on, as well as its visibility and movement in the water. Let's start with a quick overview of how the size of a fly is determined.

The fly fishing industry typically measures fly size using a numbering system, with the larger numbers representing smaller flies and the smaller numbers representing larger flies. For example, a size 14 fly is larger than a size 20 fly. This numbering system is often referred to as the "hook size" and is based on the size of the hook that the fly is tied on.

The numbering system is supposed to be standardized across the fly fishing industry, so a size 14 fly from one manufacturer is the same size as a size 14 fly from another manufacturer. But that's not always the case.

Shank You Very Much

The size of the hook is also determined by the length of the hook shank, as well as the thickness of the wire. The shank of a hook is the straight portion of the hook between the eye and the point. Hooks can have labels like 1X long or 2X short, based on the length of the shank relative to the standard length for a particular size hook.

A 1X long hook has a shank that is one size longer than the standard length, while a 2X short hook has a shank that is 2 sizes shorter than the standard length. Both retain the original size hook gap.

The length of the shank can affect the overall length of the hook and can also impact the hook's weight. A size 14 - 1x long Elk Hair Caddis would fish like a size #12. A size 16-2x short Parachute Adams would fish like a size 20.

These type of hooks are generally used for specialized flies. For instance, a Woolly Bugger or a hopper might both be tied on 2X long or 3X long hook shanks while a scud or a caddis pupae might be tied on a 1X short hook size.

Does This Hook Make Me Look Fat?

In addition to the length of the shank, the thickness of the wire can also vary among fly fishing hooks. Hooks can be labeled as X strong or X fine, based on the thickness of the wire relative to the standard thickness for a particular size hook. A 1X strong hook has thicker wire than the standard thickness, while a 1X fine hook has fine wire in comparison.

The thickness of the wire can impact a fly's strength and durability, as well as its ability to float or sink in the water column. The thickness of the wire can also affect the hook gap though it's not as much of a factor as the hook design.

It's not a hard and fast rule, but generally speaking, dry fly hooks are finer so they land softer and float easier, while wet flies, nymphs, and streamers are tied on extra strong or heavy hooks because they help the fly sink and stand up to hard fishing.

Flies like the Woolly Bugger can be tied on extra strong and extra long hooks and they fish well for smallmouth bass and large trout.

Tying it all Together

Fly fishing hooks vary in size, length, and thickness, and these differences affect the hook's overall size and performance. Hooks with longer or shorter shanks and thicker or thinner wire may be better suited for different fly fishing techniques and types of fish. It is important for fly fishermen to choose the right hook for the specific situation, taking into account the size and strength of the fish, the type of fly being used, and the fishing conditions.

If you get into fly tying you'll quickly learn that hooks for dry flies aren't the same as hooks for nymphs.  Specialized hooks help anglers match the hatch with different characteristics.

Good Old fashioned Spitballing

In addition to the hook size, the fly's size can also be indicated by its "body length," though it's less common. The length of the fly from the eye of the hook to the end of the tail is a good way of getting in the ballpark when you're trying to imitate the natural insect. This measurement is often given in millimeters or inches and can be helpful in determining the size of the fly, especially when comparing flies from different manufacturers or when tying your own flies.

Fishing flies can vary in size based on different characteristics.

Now That That's Settled...

Understanding hook size puts you in the ballpark but if you want to score with the fish there are several factors to consider when deciding what size fly to use. The size and species of the target fish, the type of water and technique being fished, and the type of food that the fish are currently eating are the main inputs.

Since we're fishing for trout, we can do away with the tarpon flies and focus on smaller offerings.

Feed Them What They Want to Eat

When it comes to fly size for trout, there are a few factors to consider. One is the size of the natural insects that the trout are feeding on. Your fly should match the size of the natural insects that are present in the river you're fishing. For example, if the trout are feeding on small midges or mayflies, you'll want to use a smaller fly. On the other hand, if the trout are feeding on larger stoneflies or caddisflies, you'll want to use a larger fly.

Getting buggy about the Correct Fly Size

Here is a general overview of the four main types of insects that are found in a trout's diet and how to tailor your fly selection to match the hatch.

  1. Mayflies
  2. These insects are common in trout streams and are an important food source for trout. Mayflies come in a variety of sizes, but most range from small (size 18-22) to medium (size 12-16). When selecting a fly to match a mayfly hatch, consider the size and life stage of the insects that the trout are feeding on. For example, if the trout are feeding on small nymphs (immature mayflies) that are in the drift near the bottom of the stream, a small (size 16-20) nymph fly may be appropriate. If the trout are feeding on larger, fully-developed adult mayflies, larger (size 14-16) dry flies may be more effective.
  1. There are specialized hatches like Drakes and Hexegenia (known as a Hex to the cool kids) that are huge for mayflies, but generally speaking, if you carry mayfly nymphs, emergers, and dry flies in the 14-20 range you'll be able to cover around 95% of the mayfly hatches you encounter.
  2. Stoneflies
  3. These insects are also common in trout streams with clean cold water and are an important food source for trout. Stoneflies come in a wide variety of sizes. When selecting a fly to match a stonefly hatch, consider the size and stage of the insect that trout eat. If trout are on Little Yellow Sally nymphs (a small species of Stonefly) for example, a small (size 14-18) nymph may be appropriate. If trout are feeding on Salmonfly adults, a size4- 6 dry fly may be more effective.
Fly fishing gargantuan Stoneflies like the Pteronarcys californica, or Salmonfly, call for massive dry flies with a long hook sh
  1. Caddisflies
  2. Caddis for short, are the most abundant insect in trout streams across the US and are a major menu item for trout. Most Caddisflies range from small (size 16-20) to medium (size 12-14). At the extreme range, the October Caddis is much larger (size 6-8).
  3. When selecting a fly to match a Caddis hatch, it's important to consider the size and stage of the insects in the drift. If trout are feeding on small larva (immature Caddisflies) near the bottom of the water column, a small (size 16-20) Caddis nymph may be the call. If the trout are feeding on emergers or dry flies a larger (size 14-16) Caddis pupae or X Caddis may be more effective.
  4. Midges:
  5. Midges are small (size 18-24) and often hatch in large numbers. They also hatch year round, making them a key food source for trout. When selecting a fly to match a midge hatch, you'll be using a very small bug (size 18-22). During a hatch dry flies will run from size 18-24 or smaller.

Understanding these bugs will help you stock your fly box so you can hone in on fly size. When selecting a fly or flies remember to match the size and life stage of the insects that the trout are eating. This is known as "matching the hatch". It's the #1 key for fly selection.

By choosing a fly that closely resembles the size, shape, and color of the insects that the fish are currently feeding on, you increase your chances of success and can create a more realistic and effective presentation of the natural food source.

The key to fly fishing success is knowing how to match the hatch. Fly sizes vary based on the bug.

In addition to matching the size and stage of the insects, it's also important to consider the type of water that you are fishing. For example, in fast-moving water, a heavier fly, an added bead head, or split shot may be necessary to get nymphs down to the fish's level. In slower water, smaller and lighter flies drift more freely and may be more effective.

A larger fly isn't always the ticket when you're fly fishing for trout. catching trout 20 inches or longer on a size 20 dry fly makes you a proud member of the 20/20 club.

Then What?

Once you get the size right, matching the pattern and color of the natural insects that trout are feeding on will increase your chances of success. For example, if the trout are feeding on light-colored mayflies, you'll want to use a fly like a mayfly emerger or dun with light-colored body and wings. And so on for any flavor of bug that trout are eating.

Be observant. Many times you can tell what trout are eating by where they are feeding in the water column. If they're feeding low, near the bottom, they're on nymphs. If they're feeding mid-river or just subsurface their probably after emergers. If you see noses out of the film they're on emergers and duns. Finally, slowly sipping from the surface film means they're likely on spinners.

Flies get more colorful and flashy as they rise in the water column. Fish darker bugs near the bottom and lighter flies up top.

It pays to be observant when you're fly fishing. Small insects are hard to see but trout behavior can tell you a lot.

So, what size fly should you use for trout?

You can usually determine the size of the natural insects trout are eating by observing the water and looking for signs of insect activity, such as emerging mayflies or rising trout. If you're not sure what size fly to use, you can also ask local fly shops or other experienced anglers for their recommendations.

If you're still not sure, try a bracketing approach. Fish a 2 fly rig, whether it's nymphs or dries and use flies of differing sizes and flavors to zero in on the bug deJour.

A size 16 PMD emerger as a dropper above a size 14 caddis larva for the point fly would be a good mix. A size 14 Caddis Pupae above a size 18 BWO nymph would also be a great choice. You get my drift (pun intended). Be methodical and find the size that fish are keyed in on.

I've had days where fish would eat different sizes and styles of fly on different drifts. Be methodical and determined. Convince yourself that every cast is going to yield a fish. Confidence on the stick is the best way to stay dialed in and catch more fish.

If you have an idea of the bug and the size and they aren't eating, go smaller. I have found that missing small will still catch fish but missing big with my bugs almost never gets it done.

Don't forget that larger fish eat tiny flies all day long. I never hesitate to throw flies in the size 20 class. Some of my largest trout have come on itty-bitty bugs and a good dead drift.

Feeding fish is easy by matching the hatch. A tiny Adams or mid size Hare's Ear will catch most trout if that's what they want to eat.  .

Putting a Bow On It

Larger flies like Hoppers and Salmonflies are a blast to cast but targeting trout with smaller flies will draw strikes during the right insect hatches.

I know flies can get spendy, that's why I asked for my first fly tying kit when I was 12 and I've been tying ever since. But, try to carry the 4 food groups (Mayflies, Caddis, Stoneflies, and Midges) in multiple sizes. Be prepared to switch if environmental conditions or the trout's behavior calls for it.

Do your homework before you hit the river. Being prepared will save you time and money. Local fly shops, guides web pages, blogs, mobile apps, and the inter-webs are great places to do some recon. That way you come stocked up with potential winners.

Once you hit the river's edge, be observant and find what the fish want to eat. That's your #1 clue to the size of fly you should be slinging. If you pay attention to the bugs on the water and trout behavior you can get dialed in pretty quickly.

If you're brand new or struggling with the process a qualified guide is an excellent investment. Not only are they on the river every day and locked in on the hatches, most guides love to share their knowledge and can teach you a lot about fly fishing tactics. With a little bit of time, knowledge, and practice you'll be able to confidently choose the best fly for the moment on your next fishing trip.

About the Author

Mike Pawlawski is a former pro quarterback and world-class fly fisherman who has dedicated his life to sharing his passion for the great outdoors with others. After an 11 year playing career starting with the Tampa Bay Buccaneers in the NFL and ending with the San Francisco Demons of the XFL, Mike hosted his own fly fishing show, "Familiar Waters," for 15 years. The Show took viewers to some of the most iconic fly fishing destinations in the world, including the crystal-clear waters of the Caribbean, the rugged rivers of the Rocky Mountains, and the expansive beauty of the Pacific Northwest. Along the way, Mike shared his knowledge and expertise with viewers, offering tips and tricks for fly fishing success and enjoying the beauty of the great outdoors.

For fly fishermen and outdoor enthusiasts looking for guidance and inspiration, Mike Pawlawski is the perfect choice. With his vast experience and expertise, he is a trusted and respected voice in the world of fly fishing, and his passion for the great outdoors is contagious. Whether you're a seasoned pro or a beginner looking to learn the ropes, Mike is the perfect guide to help you experience the beauty and excitement of fly fishing.

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