An Entomology Crash Course for the Fly Fisher
By Robert Younghanz

Although there is some debate within the entomology community as to the exact number, there is generally considered to be 13 distinct aquatic or semiaquatic insect orders, along with a variety of other aquatic arthropods, as well as worms, leeches, eels, sponges, clams, snails and mites (just to name a few other items on the menu). This is by no means an exhaustive list. To complicate matters even more, there are many insects, while terrestrial, that live near the shoreline of rivers and lakes on aquatic vegetation and the moist soil near littoral zones.
While often a very thin line, my primary goal as an entomologist, instructor and guide, has been to filter out the pertinent scientific information vital to the fly fisher and break it down so that it's understandable, thus facilitating better success and higher confidence on the water. Here is the "Cliff Notes" primer on the four major aquatic orders that will give the dedicated fly fisher a long head start.
I'm going to make this as simple as I can by focusing on EPT (no, not "Early Pregnancy Test") rather Ephemeroptera, Plecoptera, Tichoptera and Mayflies, Stoneflies, Caddisflies. I'll throw in Midges for good measure. So, let's break this down:
All insects have six legs. If you collect or see a creature with six legs it IS an insect. With that said, trout don't care since they don't know what an insect is, and they are opportunistic generalists when it comes to their feeding habits. In other words, they will eat anything they can get their mouths around given the opportunity. I once saw a trout eat a cigarette butt; the cigarette butt flies I tie up are second to none.
Let's start with Mayflies. As nymphs, mayflies have three tails and one hook on each appendage. Although fairly infrequent in the context of the entire order, there are a small percentage of mayfly nymphs that do have two tails. All adult mayflies have wings that are held vertically when at rest, like a sailboat. During a spinner fall, after they have mated, you will see dead mayflies with their wings sprawled out flat on the water, on each side of their thorax. A little-known fact about mayflies is that virtually all of them have four wings. Although not usually visible to the naked eye, they have what are known as sub or hind wings, which are reduced in size as compared with the main set of wings. I'm not suggesting that one would tie their mayfly adult patterns any differently due to this taxonomic feature, but it does make for good conversation at cocktail parties and TU meetings.
Stoneflies are a piece of cake - Nymphs, 2/2, two tails and two hooks on each of their appendages. NO EXCEPTIONS. As adults, their wings are pleated and lay on top of one another flat on their backs no matter their size or color. Again, no exceptions. Two orders done!
Caddisflies, i.e. "case makers" (a misnomer), will either be in cases or some type of other larval housing, or free-living, but will always look like little caterpillars in a multitude of colors. As adults, they have tent- or roof-like hairy membranous wings, an aquatic moth, if you will.
Lastly, midges-in the order of Diptera, which incorporates all flies, aquatic or terrestrial. Midges are just one family of many aquatic flies and as the nomenclature tells us, they have two wings. "Di" meaning "two" and "ptera" meaning "wings" usually divergent and mosquito-like in their general appearance as adults. As larva, they look like small white, off-white or red worms (thus the term "red rock worm") or strands of red or white string.
Believe it or not, it's really that simple. Now that you can begin to separate your key aquatic orders, the next step is to go out and collect trout foods on your own and begin the process of determining just what type of mayfly, stonefly or caddisfly you're looking at and what type of bugs the fish are eating. Not only is this fun, but it all makes you a better angler!

Robert Younghanz, a.k.a. The Bug Guy, is an internationally known fly-fishing guide and instructor.