Entomology, approach and other “disturbing” notions…

Entomology: Perlidae

Entomology:  why a “disturbing” notion?

Because its high value in flyfishing tends to “disturb” the angler from the cast and the catch of his quarry.

Entomology is without any doubt a wonderful science and its knowledge is of great help to flyanglers. However, this “article” is intended for beginners and its goal is to attract more and more people to flyfishing avoiding any complexity. For this reason, let’s start from the simplest points.

Going deeply into entomology is not compulsory for the flyangler.

For the beginner, being able to understand the difference between mayflies, sedges, stoneflies, terrestrials and midges is much more important than being a true expert.

They are all insects – except terrestrials – having a life cycle starting from an egg laid under or on the water surface and developing into adult through a more or less complex metamorphosis. Mating, egg laying and death of the insects close their life.

“Groups” of insects

Distinguishing the various “groups” of insects, especially during their adult stage, is rather easy. Basic entomology helps a lot at this stage.

  • Ephemera (mayflies) have their wings in vertical position (V),
  • Trichoptera (sedges or caddis) show their wings tent-like (/\)
  • Plecoptera (stoneflies) keep them flat on the back (____).
  • Midges are similar to mosquitos while
  • Terrestrials have different shapes and colors: they represent all those small insects not living in the water and which may fall on to the river surface by accident (wasps, bees, crickets, butterflies, ants, caterpillars, grasshoppers…).

Ephemera danica, Ephemera guttulata, Ecdyonurus venosus, Baetis rhodanifor example – are all Ephemera. They are different in size and color and this may be an important clue in the choice of our fly.

Entomology helps us identify the male from the female but it is not as important. We should concentrate mostly on the shape, the size and the color.


Fishing with the imitation of a Sedge when fish rise on Ephemera is nonsense. That’s why we should be able to detect “what” fish are feeding on.

Some anglers, however, belong to another “school”. They consider this kind of identification extremely important and give attention to color and hues of the insect, choosing a fly matching all these details. It’s an interesting point of view which, however, has a weak point.

Entomology teaches us that in most cases, the under part of the body of natural flies is lighter than the above half. This is Nature’s camouflage. Predators attack from below and a light body helps being not detected from a distance against a bright sky.

In spite of this, when tying our flies we copy the upper part of the insect’s body or its overall color (greenish, yellowish, reddish, brownish…) thus obtaining an artificial which does NOT match the natural properly. We reproduce the UPPER side of the body, not the LOWER.

There is another point increasing confusion.

Brian and Goddard, in their “The Trout & the Fly” (*), give us an important clue:

Brian and Goddard, "The Trout & the Fly" Brian and Goddard,  "The Trout & the Fly"

Seen from below, the color of the body tends to be very dark. Where is the truth?

  • a) if we have to match the insect for a perfect imitation, the lower body should be light
  • b) if we have to match what the  fish see, the lower body should be  dark .

Quite puzzling, isn’t it?

What should do?

As a matter of fact, this is NOT very important to the fish’s eyes because we DO catch fish with “wrong” imitations. So, why do we catch fish? For sure, not only because of the color. Fish are not scientists nor scholars and feed on anything they consider eatable. They don’t care Latin names and/or color hues.

There are many exceptions to the above theory (particular water or light/sky conditions, extremely shy or overfished fish…). In most cases our success is due to a proper presentation, the delicacy of the cast and to the correct path followed by our fly. In other words, the fly should go where fish expect it to be.

Basic colors have their importance but hues or shades haven’t. Fish see the fly against the sky or the sun. When they approach the insect from below they see but a black or dark shape of the fly. Color and hues are undistinguishable.

The important point is that WE must be able to see the fly, to detect it during its downstream trip and be ready to strike. For this reasons flies should be first of all visible to the angler, with a clear, white part or wings if we fish darker spots or in dim light conditions. Of course, a dark wing will be useful in bright water.


Fish have a good sight but not so extreme and are not able to notice the difference between thin or stronger tippets (within a certain range). Many anglers insist on the importance of a 0,08 mm against a 0,12 mm.

If fish were able to note such a small difference (0,04mm!!!), they would also spot other details:

  • the hook point entering the water
  • the exceeding number of tails of our artificial fly
  • the last part of the tippet protruding from the hook eye and laying onto the water surface
  • the abundance of “legs” (insects only have 6)

Water disturbance is probably more important than a “perfect” fly.  Stepping into the water should be avoided if unnecessary. If we are somehow obliged, wading should be as careful as possible, to avoid the propagation of sound or noise through the water and river bottom.

To finish with, a question which may arise a tornado: can be flies considered specific for certain fish? In other words: are there flies for trout, flies for chub, flies for grayling, etc?

Let’s suppose a river contains all the above fish in the same pool or riffle and we are fishing with a Bivisible, mostly considered as a fly for chub. Should the above question be positive, we would not catch trout and grayling but chub only.

The same is if we use a Red Tag (considered as a grayling pattern by most anglers): neither the trout nor the chub should accept it.

This never happens: fish feed on what they find on the water, if considered edible, and don’t refuse a certain pattern simply because WE consider it for a specific fish.


Of course, all the above refers to dry flies. Wet, Nymph and Streamer fishing happens under the water where light reflection, movement and reaction are completely different.

Flyfishing is not – and never has been – an exact discipline and any day you may find something new, in spite of your long lasting experience. The more you keep things clear and simple, the more your knowledge will increase and the more fish you’ll be able to catch.


(*) I owe a lot of the above to Clarke’s and Goddard’s “The Trout and the Fly, a New Approach”,  1980, which I had the honor and pleasure to translate into Italian.

A useful approach to Entomology

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