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For beginner anglers, flies can be an overwhelming topic to digest. With literally thousands of fly patterns available - all with different names - knowing where to start can seem impossible. We’re here to simplify this important topic. Today, we’ll discuss what a fly is, introduce some basic terminology, and categorize flies into 4 distinct categories. By the end of this guide, you’ll be able to look at a fly and make a confident assessment of what type of fly it is, and how it should be fished. To keep things really simple, we’re only going to focus on flies for trout in freshwater rivers and streams. Keep reading to learn all about fly fishing flies in this helpful guide.

What Is A Fly?

First things first, what is a fly? Non-anglers might think of houseflies when they hear the word ‘fly’, but for anglers, it means much more. For starters, we should discuss some basic terminology. In fly fishing lingo, 'flies' are essentially our 'lures'. Flies are artificial baits that can imitate a variety of trout prey such as aquatic insects, smaller fish, eggs, worms, scuds, grasshoppers, and much more. There are essentially no limits to what a fly can imitate, and as fly fishers, we love this because it means that anything a trout eats, there is probably a fly to mimic it.

To be considered a fly, the only criterion is that it uses thread to tie materials to the hook and can be cast with a fly rod. Therefore, casting a Rapala with a fly rod does not make the Rapala a fly, because it doesn’t use thread to tie materials to a hook. Some debate exists over whether flies without threaded materials should really be considered 'flies', but that’s not a rabbit hole we’ll go down today.

This brings us to our next point: fly patterns. If a fly is an artificial bait using thread and materials on a hook, then a fly pattern is any one specific “model” of fly. Every fly pattern uses materials and a tying recipe specific to that one pattern. The Parachute Adams, for example, is a long-standing, effective fly pattern. The sheer number of fly patterns available is cause for overwhelm, but in our next sections, we’ll categorize them to make things easy.

Basic Entomology

Let's briefly touch on aquatic entomology—the study of water-dwelling insects—before exploring the four categories of flies. Having a very basic understanding of entomology will greatly help you comprehend the fly categories, as well as build a foundation for further learning as you discover hatches on the water.

To start, we should first understand that most of what we imitate with our flies is aquatic insects, meaning bugs that live the majority of their life underwater. There are obvious exceptions to this, such as baitfish, grasshoppers, etc., but generally speaking, we’re imitating bugs.

Aquatic insects undergo a life cycle similar to all bugs, where they begin as an egg, hatch into a “nymphal”, or immature stage, and finally emerge as an adult before reproducing. This life cycle is observed in caterpillars (immature stage) building a cocoon and emerging as a butterfly (adult stage). Entomologists call this life cycle metamorphosis, and there are actually two different types of metamorphosis that we see in aquatic insects, but let's keep it simple for now.

Knowing that aquatic insects undergo metamorphosis is important to fly fishers because we imitate 3 key phases of their life cycle. We imitate the nymphal, or immature stage, the emerging (or sometimes called pupating) stage, and we imitate the adult stage.

Why does this matter? Let’s say a trout is rising to the water’s surface, feeding on adult insects as they hatch. The trout is in a rhythm, gulping bugs from the surface film every 30 seconds or so, and then submerging just a few inches below the surface. This fish is actively feeding on top, making this a great opportunity to use a “dry fly”, which is a fly that floats on the surface and imitates adult insects. Conversely, this would not be a good time to use a “nymph”, which sinks below the surface and imitates immature bugs. A nymph would likely drift below the surface-oriented trout and go unseen.  As you can see, knowing just a little bit about entomology, and being observant, can lead to the correct fly choices, and therefore to many more trout caught.

Fly Categories

Now that we know what a fly is, what a fly pattern is, and the basic life cycle of aquatic insects, we’re ready to categorize our trout flies. Our four categories are; Nymphs, Wets/Emergers, Dry Flies, and Streamers. These categories will cover about 99% of trout flies, and we’ll discuss a few exceptions to them later on. For now, let's go through each category, and learn what characteristics define each fly type.

Nymphs

Nymphs imitate the nymphal, or immature stage of an aquatic insect. Because of this, nymphs are always fished subsurface, meaning we want them to sink. To achieve this, many nymphs are tied with a weighted bead head. Beads can be made of brass, copper, or tungsten, each offering varying sink rates to achieve depth quicker or slower. Other patterns may use lead wire wraps around the hook shank to achieve weight. Finally, some nymphs are tied unweighted, so they are typically fished with split shot on the leader to help them sink.

Nymphs come in a wide variety of sizes, weights, and colors, depending on what insect they imitate. Distinguishing a nymph from other fly types is usually pretty straightforward. If it has a bead head and a sparsely tied body (void of bushy feathers or longer fibers), then it’s probably a nymph.

Fishing nymphs can be done under a strike indicator (bobber), under a dry fly, or using tight line techniques. Generally, nymphing warrants a “dead drift” meaning you want your flies to be drifting at the exact speed of the current. Whether you’re using an indicator or tight-lining, you generally rely on some sort of visual aid (a bobber) or tactile feel (in the case of tight-lining),  to alert you to a strike since you typically cannot see the fish eating your fly below the water’s surface.

Wets/Emergers

Wet flies and emergers are somewhat interchangeable terms that refer to flies that imitate the emerging (or pupating) stage of an aquatic insect’s life cycle. This is when a bug transforms from a subsurface insect into a winged adult that you’d see flying around the river. This period of an insect’s life cycle leaves them extremely vulnerable to predation from trout, as they leave behind their safe residence underneath rocks and sticks, and drift upward in the water column toward the surface.

As anglers, we look forward to this emergence because it usually means that trout will be actively feeding on vulnerable emerging bugs somewhere in the middle to upper part of the water column. In short, wets/emergers are neither nymphs nor dry flies, but something between the two.

Many wets/emergers look similar to nymphs, although they usually feature longer feathers or fibers that imitate an insect's legs, wings, or nymphal shuck. Some wet flies are weighted with a bead head, and others are tied unweighted. Knowing whether to use a weighted or unweighted emerger depends on how deep the trout are feeding on natural emergers. Again, observation will lead to more effective fly selection.

Fishing a wet fly can be done in several different ways. A common technique is to “swing” the fly as it drifts downstream of you. The tension created in your line and leader as you swing the fly through the current results in an upward movement in your fly toward the surface, imitating an emerging insect. You can also fish emergers the same way you’d fish a nymph, by dead-drifting it under a strike indicator or a dry fly. Depending on how you fish an emerger, you’ll again rely on a visual aid or a tactile sensation to alert you to a strike. In some rare cases, you may be able to see a strike, if your emerger fly is very near the surface of the water.

Dry Flies

Dry flies are surface patterns that float, imitating adult insects on the water's surface. When insects hatch, there is usually a brief moment when they must float on the surface to dry their wings before they can fly away. This leaves the bugs very vulnerable to predation, as trout can rise to the surface and slurp them down by the mouthful.

Seeing adult insects on the surface is one of the most exciting prospects for a trout angler, especially if fish are rising to eat them. This is because fishing dry flies is extremely visual, and casting dry flies is fun! Fishing dry flies is probably what most people think of when they envision fly fishing for trout. It’s the “purest” form of fly fishing for many anglers, and once you experience it firsthand, you’ll understand what all the hype is about.

Dry flies are often tied using hackly feathers, deer or elk hair, or buoyant synthetic materials like foam or polypropylene yarn. Remember, dry flies are designed to float, so they need to be lightweight. Because of this, they can appear fragile or even dainty, and they won’t have a bead head or any added weight.

Fishing with dry flies usually necessitates a dead drift on the surface. Depending on factors like the size of the river and where the trout are rising, you could be casting your flies directly upstream of yourself, quartering upstream (casting at a 45-degree angle), casting across (casting perpendicular to the current), or quartering downstream. Every situation is different and you should adjust your technique based on your observations. Sometimes, “skating” or twitching your dry fly can be a productive technique, as some insect species, such as caddis, will skitter around on the water’s surface.

Streamers

Streamers imitate smaller fish, which could be juvenile trout (yes, trout are cannibals), sculpins, minnows, chubs, or a plethora of other smaller or juvenile fish species. Trout are predatory creatures that will eat smaller fish when given the opportunity, and as fly fishers, we take advantage of this by fishing with streamers.

Distinguishing a streamer from other types of flies is usually pretty easy. For starters, streamers are usually bigger, roughly anywhere from 1 inch to 7 inches long, depending on what they imitate. Secondly, streamers often incorporate long, flowy materials such as marabou, tinsel flash, or rubber legs. Lastly, streamers are frequently weighted, featuring cone heads, bead heads, or dumbbell eyes. In short, if it looks like a small fish, it's probably a streamer.

Fishing streamers can be a very interactive experience, or it could be more passive, similar to swinging wet flies. The active approach would involve “stripping” the streamer, which means to retrieve the streamer toward you giving it the appearance of fleeing from predatory trout. This is a common technique used in drift fishing, where anglers will cast their streamers along the bank and strip them back toward the boat in hopes of enticing a trout that’s waiting to ambush prey along the bank. We call this technique “robbing the bank”, and it's an extremely exciting and visual way to fish for trout. The more passive approach of swinging a streamer is a great technique for wade fishing when you’re constricted to smaller sections of water that should be fished more thoroughly. Generally, you’ll cast your streamer quartering downstream, and let the current swing the fly toward the bank downstream of you. Then you can make small strips or twitches of the fly before taking a couple of steps downstream and repeating the process. With each swing you’re fishing new water, slowly working your way downriver and presenting your fly to unsuspecting trout.

Exceptions

Now that we’ve covered the 4 main categories of trout flies, we should discuss some exceptions. Not all trout flies will land firmly in one of these 4 categories. Take a mouse fly, for example. A mouse fly pattern imitates a mouse swimming on the surface of the water. Since it’s a surface fly, you could call it a dry fly, but it's generally not dead-drifted, and it's certainly not an insect, so, therefore, it falls into a unique category of its own. The same could be said for patterns like frogs and crayfish, which exhibit behavior that’s unique to them. Although these exceptions fall outside of the 4 fly categories, they’re still relevant and shouldn’t be overlooked when conditions warrant trying them. As we’ve mentioned several times, be observant and do your best to imitate the natural trout food you see around you!

It’s also worth briefly mentioning fly categories other than trout flies for rivers and streams. When you start looking at flies for saltwater, warmwater, and stillwater, the fly categories can change entirely. In saltwater, for example, there aren’t aquatic hatches, per se, so dry flies and nymphs are not going to be effective. Instead, you’ll use flies that imitate salty critters like shrimp, crabs, and baitfish. All this is to say that as you progress beyond trout fishing in streams, your fly selection will also need to evolve to match the predominant food sources of the fishery.

Matching The Hatch

You may have heard the phrase “match the hatch” before, and you might be wondering what this means. Match the hatch refers to matching your fly pattern to the specific species of insect that’s hatching at any given time.

Matching the hatch can be important when trout are focused on a specific insect emergence, often ignoring any fly that doesn’t accurately match the natural insects' size, profile, and color. This can be extremely frustrating if you aren’t fishing the correct pattern because you can see trout feeding, but you can’t entice them to take your fly.

There are two ways to overcome this challenge, and they go hand-in-hand. The first thing to do is to be observant of the insects hatching and pick a fly that resembles their size, profile, and color as closely as possible. We recommend prioritizing your fly selection by size first, profile second, and color third. In doing this, you might be able to pick a fly that’s just close enough to the naturals to fool a fish. The second step to matching the hatch is to continue learning about aquatic entomology. You certainly don’t need a collegiate-level course to be an effective fly angler, but it behooves you to understand the common families of aquatic insects: Mayflies, Caddisflies, Stoneflies, and Midges. As you become familiar with each family, it becomes easier to identify the bugs you see on the river, and thus, easier to pick an appropriate fly to match them.

Attractor Patterns

Inevitably, there will be times when nothing obvious is hatching - usually more often than not. This can make fly selection a little tricky, because you may not be sure what fly to pick. This is when attractor patterns can be a good choice. An attractor pattern is a fly pattern that may or may not imitate a specific insect, fish, or trout food, but rather relies on bold qualities such as its large size, bright colors, or flashy appearance to get the attention of otherwise lethargic or uninterested trout. A common example of an attractor pattern is a Frenchie nymph, which looks somewhat like a Mayfly nymph but incorporates a sparkly collar behind the bead. Real Mayfly nymphs do not have flashy collars behind their head, but trout seem to react well to this feature and will readily eat Frenchie nymphs when other, more realistic flies, are not working.

Attractor patterns are not limited to nymphs. Below are examples of a dry fly attractor and a streamer attractor. As you can see, attractor patterns can still fall within our 4 fly categories, and they’re worth mentioning because they can be very effective when more realistic patterns are going unnoticed.

Fly Sizes

The final topic we’ll cover is fly sizing, which is technically the size of the hook that the fly is tied on. When you go into a fly shop and peruse the fly bins, you’ll notice that individual fly patterns are offered in various sizes. Each fly bin will be labeled with a numerical size, with smaller numbers being bigger flies, and bigger numbers being smaller flies (fly fishermen love to make things complicated). A size 4 grasshopper fly, for example, is a rather large dry fly. A size 22 nymph, however, is teeny tiny - don’t drop it on the carpet!

So now you’re probably wondering how to decide what size fly to use. This mostly depends on the size of the naturals you’re trying to imitate. Let’s say you’re out fishing and you notice some caddis starting to hatch. You know they’re caddis because you’ve done some research about the common families of aquatic insects, and these bugs fit the physical and behavioral descriptions of caddis. You’re able to inspect a caddis up close as it rests on a willow, and you make a mental note of its size. Now you can pull out your fly box and select an elk hair caddis that looks roughly the same size as the natural you observed. Once again, observation leads to smarter fly choices, and therefore more fish caught.

If you don’t see anything hatching, another option is to carefully wade into the river and pick up a stone to see what aquatic insects are clinging to it. This can give you some indication of what nymphs are present in the river, and perhaps lead you to a nymph fly in your box that closely resembles their size (and profile and color). Some anglers may argue that this doesn’t necessarily tell you what bugs the trout are feeding on, so you gain little from the exercise. Although there is some truth to this argument, we’d argue that you know more by flipping rocks than if you hadn’t, so at least you’ll make an educated guess rather than picking a fly at random. Additionally, observing aquatic insects in their nymphal form is incredibly fascinating. You’ll be surprised at how much life exists beneath the water’s surface!

Lastly, don’t be bashful and simply ask the fly shop staff what they suggest. Chances are they know the hot flies for where you’ll be fishing, and in what sizes to get them.

Understanding fly (hook) sizes is part of fly fishing and will help you when shopping for flies, organizing your boxes, and talking with other anglers. If someone tells you they had great luck on a size 4 grasshopper, you’ll know what they mean and can try it for yourself. Next time at the fly shop, note the fly sizes as you browse. After a while, you’ll be able to look at a fly and estimate its size relatively accurately.

Conclusion

Congratulations! You're now familiar with fly basics, including the four main categories of trout flies. This knowledge will boost your confidence in selecting the right flies at the shop and along the river. Understanding flies and when to use them is an important step toward being a successful, self-sufficient angler. As you continue learning more about flies and their uses, your enjoyment of the sport will also grow. Just remember, everyone was a beginner fly fisher at one time, so you shouldn’t feel embarrassed if you don’t know what fly to pick, especially when you’re new to the sport. Even veteran anglers will be stumped more than they care to admit, and that challenge is one of the most enthralling aspects of fly fishing. By far the best teacher is the river itself, so we encourage you to get out on the water, observe, and fish. Don’t worry about making mistakes, because that’s how you learn. Enjoy your fishing adventures and stay safe out there!

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Questions?

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