Is That Fly a Nymph? A Look At Insect Life Cycles

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Midge Emergence Photo by Louis Cahill

Midge Emergence Photo by Louis Cahill

Is that fly a nymph? That’s the question I got from a reader the other day.

A fair question from a guy who’s only fly fished for redfish and isn’t familiar with trout flies. A simple question with a very complicated answer. Complicated enough that I figured it deserved an explanation, and why not share it.

The fly in question was a midge pattern, so technically not a nymph.

The word “nymph” however, like so many words, shares two meanings. The literal (denotative) meaning is a juvenile mayfly or stonefly in the subsurface phase of its life cycle. The word is also used to refer to flies that imitate these insects. Since a midge starts its life as a larva rather than a nymph, the flies that imitate them are not technically nymphs.

The word nymph also has a conversational (connotative) meaning. It is often used to refer to flies that are dead drifted below the surface. A San Juan Worm or an egg pattern is often referred to as a nymph because of the way they are fished. Some folks will use the term “wet fly” for any fly fished below the surface but this is not correct either. Wet flies are a specific style of fly intended to be fished in a different manner. So describing the midge fly as a nymph, while inaccurate, is not necessarily wrong. It can be fished as a nymph, connotatively.

I’m not generally one to engage in exercises of semantics but I believe there is more at stake here than clarity of the word. I know that when I first became aware of midge patterns many years ago, I was reluctant to fish them because they were unfamiliar. Words like larva and pupa kept me away from these patterns and the fish who eat them. I would, for example, fish a caddis dry fly frequently but never a larva or pupa.

I don’t think you need to know the Latin names of the insects. That’s fine for the guys who get into it but in the words of Bob Dylan, “it ain’t me babe.” I have friends who are skilled and experienced fly fishermen who will spot Stenonema interpuntayum in the air and say, “the Light Cahills are hatching.” And can you blame them? I had to ask Kent for the Latin name just to write that sentence! I do however think a basic understanding of the insects we imitate is crucial. Trust me, this will be very basic.

The stages of a mayfly’s life cycle of interest to anglers are as follows. Nymph, the aforementioned subsurface juvenile. Emerger, the stage when the nymph rises to the surface and sheds his shuck. (it’s worth mentioning that for some insects this does not take place in the water.) Adult, the sexually mature insects which fly around our heads. Spinner, the adult who has mated and collapsed on the water to die. Stoneflies follow a very similar cycle.

Even the slightest thought on this life cycle will yield valuable information for the fly fisher. For example, notice that I describe the adult mayfly as flying around your head. This immediately begs some questions. Are you fishing enough emergers? How often does a fish get the chance to eat an adult? Should you be tying more cripple patterns?

Midges and caddis have a different life cycle but the basics, as they apply to the angler, are much the same. The larva, generally a small worm of sorts, is much like the nymph and is fished in the same way and under the same circumstances. The pupa is kind of like the emerger. It’s the phase when the larva becomes an adult. Hence the caddis emerger. The adult, same as the mayfly. I’m sure there are midge spinners or something close but I don’t know anyone who’s worked out that pattern.

So back to the readers question. The fly was technically a midge pupa, defined by its wing tied to represent the rising air bubble. It is very effective fished in the film when midges are hatching. (Another misnomer. They are emerging, not hatching.) This fly is however just as effective fished with split shot as a nymph. Simple answer.

The more you know about the insects you imitate, the more effective you will be as an angler. For example, knowing that stoneflies have a two-year nymphal cycle and thus are always present in streams where they live as nymphs, I generally employee a stonefly pattern when searching for fish. A tiny piece of information that I use effectively almost all the time.

There are a great many books on the subject, not least of which in Al Caucci and Bob Nastasi’s “Hatches II” which is very detailed and informative but reads like a text book. A wealth of information if you have the patience for it.

http://www.amazon.com/Hatches-II-Complete-American-Streams/dp/1592283225

A more digestible and brilliantly photographed version is the “Bugs of the Underworld” DVD by Ralph and Lisa Cutter. The videos below are from their YouTube channel. They are excerpts from the DVD. These videos are amazing! Incredibly informative and the photography is mind blowing. You can check out the Cutter’s videos, books and fly fishing school at http://flyline.com/

Louis Cahill
Gink & Gasoline
www.ginkandgasoline.com
hookups@ginkandgasoline.com
 
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6 thoughts on “Is That Fly a Nymph? A Look At Insect Life Cycles

  1. The ephemeroptera(mayfly) will emerge as a subimago or a dun and is not sexually mature until it molts one more time and becomes a spinner. They may hide out in trees and shrubs for 12-24 hrs before molting and then after becoming an imago (adult/spinner) and form a mating swarm and after reproducing will die becoming ‘spent’ and a great food source for trout and birds alike. Mayflies go thru an incomplete metamorphosis because they don’t undergo a pupal stage. Stoneflies usually crawl out of the water and molt from their nymphal skin or naiad, morphing directly into the adult stonefly we know.
    Tight Lines,
    Koz

  2. In the spring and fall with a sampling net in my hand they are larva, pupae (for some reason we do not count pupae when scoring streams) nymph and adult.

    Now with a fly rod in hand, if it drifts its a nymph, if it’s stripped its a streamer.

  3. In teaching fly fishing to vets for project Healing Waters and scouts for Fly Fishing merit badge, it is easy to overwhelm the novice with technical jargon and names that are not necessary to enjoy the sport. Overcoming the fact that our students do not know the difference between a dry fly and one fished under the surface or even under the surface film is important to be able to successfully teach. Thus, I agree with everything you said and appreciate your “no nonsense” descriptions of what folks should know to be more effective fly fishermen. In our neck of the woods (North Georgia), reliable, visible hatches are much less prevalent and prospecting is almost always the order of the day. What many folks don’t get is that knowledge of the life cycle of bugs fish are eating is a key element for success because it determines how you prospect and what flies you use to prospect.

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