What They’re Eating Pt. 1 – Choosing the Right Fly (Subsurface)


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By Andre Egli

I’m about to ask you to do something really difficult, but trust me it’ll be worth it.  You’re standing on the banks of a river. You just put your waders on and you see a very promising looking pool, all you want to do is tie on your favorite fly and start casting.  STOP!  I’ve been in this situation numerous times; you just want to start fishing I totally get it.  However, you have no idea what the fish are feeding on.  You might be able to catch a fish or two by tying on what worked yesterday or using an attractor pattern, but in the long run you’ll catch more fish if you take a moment and study the river.  There are two ways to do this:

  1. Turn over some rocks and see what aquatic insects are present in the river.
  2. Watch the rises of the fish in the river.

This week’s post will focus on number 1 (subsurface) and next week I’ll dive into number 2 (top water).

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Matching the Hatch

As much fun as it is to catch trout on dry flies, the vast majority of what a trout eats is subsurface nymphs and larva.  In fact, when trout are feeding 90% of the food they consume is subsurface, so knowing what’s dwelling under the water is imperative to catching more fish.

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Checking for Aquatic Insects

It’s very easy to figure out what insects are in a river, simply grab a stone from the river bed and turn it over.  The best place to do this is in a shallow area with fast moving water.  These areas tend to be more oxygenated and insects thrive here.  Pick up a stone and turn it over, the underside will be teaming with insects.  Take a moment to identify what you see.  Often times you might see several different types of insects.  In this case try an imitation of the most prevalent insect and if that is unsuccessful switch to an imitation of another until you find what’s working.

When you’re trying to match a fly in your box with an insect in the river, the three most important things to consider are; size, shape, and color in that order. It’s not necessary to know the scientific name or genus of the bugs you see, just what it looks like.  I did a post a while back about casting multiple times and shared a subsurface video of what trout see in a flowing river.  They don’t have a tremendous amount of time to critically look at your fly and see if it perfectly resembles the mayfly nymphs they’ve been eating all morning, so you don’t have to match the insect perfectly.  However, you do need to be in the ballpark and those three guide posts will help.

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Aquatic Insects

Size is pretty simple.  Find a fly in your box that is generally about the same size as the insect you’re trying to imitate.

Shape comes next.  Some aquatic insects have curved bodies, some are straight, some have very pronounced body sections, some have very pronounced legs, etc.  Try to find a fly that matches the overall shape of the insect you’re trying to imitate.

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Corresponding Flies to Match the Hatch

Finally, color.  Color is the least important variable but can still make a difference.  If all the stoneflies you find under rocks have a yellowish tint to them and you start casting a black imitation that matches the size and shape, you’ll likely catch fish just not as many as you would with a yellow imitation.  Color should also be considered based on water conditions.  If the water is crystal clear muted tones will work just fine.  If the water is a bit cloudy, brighter more reflective patterns will tend to work better.  For example, you won’t turn over a rock and find something that looks like a Zug Bug, but this fly works wonders in cloudy murky water.

If you can manage to take those few extra minutes to look under a rock or two and see what’s swimming around, I promise your day will be much more successful.  Also following the simple guide of matching size, shape, and color will dramatically increase the number of fish you catch.  Next time, I’ll dive into identifying what fish are feeding on based on their surface rises, but since 90% of what they eat is subsurface I thought it was best to tackle this first.  Now get out there and give it a try!  Until next time, happy fishing!

–          A. Egli

Categories: Fly Fishing, TipsTags: , , , , , , , , , , , , , , , , , ,

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