Fly Fishing Tips – Learning Which Fly to Use

Learning Which Fly to Use

fly fishing photo emerger in rainbow trout

The artificial flies used in the sport of fly fishing can be one of the most confusing aspects for beginners to understand and learn. There are literally hundreds or thousands variations of artificial flies, and knowing which fly to use can be rather tricky. If you want to become an expert fly fisherman you need to learn as much as you can about the type of flies used to catch fish.

Learning about the different types of flies used to catch fish on a fly rod can be a daunting task at first, but like everything in fly fishing it is a process. And every process starts with a first step. If you want to learn how to determine which fly to use in any particular fishing situation, you have to start developing a basic understanding of aquatic insects. There are two parts to this process.

The first part involves learning what types of flies are living in your fishing environment. There are many, but the three most common kinds of aquatic insects imitated by fly fishermen are mayflies, caddis flies and stoneflies. Look up what kinds of insects live in your local stream. Look at some pictures. Get into the river and flip over a few rocks.

Use a small net to capture hatches of insects and take a look. When you use an artificial fly you are essentially imitating three things from a natural fly: size, shape and color, in that order. Start with your local stream and find out what types of insects you will be imitating.

The next part involves learning how to present your artificial imitations so that they look natural enough to trick a fish into eating them. This is referred to as your presentation and if it is not good you won’t catch many fish! Learning how to present different kinds of artificial flies means understanding the life cycles of aquatic insects.

Here are some basic keywords you will have to know: egg, nymph, emerger, dun, spinner and adult. When you are at your local fly shop looking at the various flies, you may notice these names. For example, you could buy a caddis fly as a dun, as an emerger, as a spinner and even as a crippled spinner. How do you know what makes these flies different from one another and when do you use each one?

Each version imitates a part of the bug’s natural life cycle. Learn to this life cycle and recognize which part is happening in front of you on the river and you will know which fly to tie on to be successful.

fly fishing photo mayfly life cycle

 Here is rundown of a basic aquatic insect life cycle. We will use a mayfly as an example.

  1. Mature females called spinners lay their eggs on the water’s surface. These eggs hatch, producing very small larvae.
  2. The larvae turn into nymphs. Nymphs are the underwater juvenile version of an aquatic insect and it is where they will spend 90% of their lives. Nymph fishing also represents a very large part of a fly fisherman’s life, because it is where most fish will be eating. Flip over a few rocks in your local stream and find a few nymphs to see what they look like. They are ugly, prehistoric-looking insects. Some nymphs cling to rocks, some burrow into the silt and others swim. It depends on the species and the location. As time passes nymphs will grow and molt their exoskeletons several times.
  3. Once the nymph reaches a certain point in their life cycle, they will migrate to the surface of the water and emerge as actual flies. This is called the emergence stage and is why certain artificial flies are called emergers. Emergers are especially vulnerable to being eaten by fish, a fact that you can use to trick fish into eating your artificial fly. The emergence stage is very fast and it occurs as the nymph moves upward towards the surface and ends when the nymph molts to expose themselves as a bug with wings. This winged bug is now called a dun.
  4. The dun will sit on the surface of the water for a few minutes, allowing its wings to dry. This also makes it vulnerable to being eaten (another reason to keep dun-versions of flies in your box). If it is not eaten the dun will eventually fly away to some river-side vegetation, where it will molt several more times until it is an adult. Adult mayflies only live for a few days.
  5. Adult mayflies become spinners and the males and females meet at the surface of the water to mate. Then the female spinner lays her eggs on the water’s surface the entire life cycle starts all over again. After mating both spinners die on the surface, where greedy fish come and get them.

If you have a good understanding of what these insects look like (their size, shape and color) and you can identify what part of their life cycle is currently going on, you will know exactly what artificial representation you should tie on to successfully catch feeding fish.

Tight lines!

David Darling

As always, your comments and opinions are welcome and encouraged.

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  1. Gunner Teaster says

    I am new to fly fishing and i use mainly nymphs. I know there are trout in some pools on the new haven river in vermont because i usually scare them. What is the best presentation for deep pool when using nymphs where you know some trout might be? also do rainbow and brookys hide in the same type of places or should i look in different spots? Also with slow moving current next to the bank, is it good to upstream cast and animate it or upstream cast and let it float? also how long on an upstream cast should i let it float before recasting?

    • David says

      Thanks for the reply.

      I do not have the expert know-how to answer all of your questions.
      A lot of the answers depend on what season it is and what size & type of gear you are using.

      When I have a question I will post the question to Twitter (it really works) and usually get some great responses.
      Do a Twitter search for “nymph fishing” or “casting upstream” to find the experts.
      Remember to put your keywords in quotes so the words will be searched as one word instead of two separate words.

      Also, I go to some fly fishing blogs & forums.
      Here are 2 I use frequently.

      I hope this helps.

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