What are they taking?” It’s one of fly fishing’s most frequently asked questions, and for some anglers, the search for the fly hatch answer is one of the most fascinating elements of the sport.
The majority of fly fishers, however, spend little time matching the hatch. They simply match a natural food’s form, such as the upright wings of a mayfly dun, and then fish with form-suggestive patterns like an Adams dry fly, or when imitating nymphs, a Hare’s-ear or Pheasant-tail Nymph.
But for die-hard hatch-matchers—or amateur entomologists—a simple approach doesn’t satisfy. These anglers are in search of a greater understanding of the coldwater ecosystem they call their home stream, and they want to know exactly what trout foods exist and learn everything they can about them. With this knowledge, they can predict and anticipate major insect emergences and be ready with precise imitations. Hatch-matchers don’t just want to match wits with the most selective trout; they want to outdo them.
Learning more about what trout eat will increase your knowledge and change your entire approach to the game. For example, once you identify the insects on your home water, tying flies to match those specific naturals becomes more focused and purposeful. There’s also more to do onstream when you’re a hatch-matcher. Instead of tying on a fly and fishing right away, your first moments onstream are spent observing, looking under rocks for nymphs, peeking into the woods for resting adults or spinners, and simply watching the sequence of an emergence unfold. You develop a whole new system catered to your observations.
Start by learning about mayflies because on many streams, they make up the bulk of a trout’s diet. When you have mayflies mastered, move on to other important food sources like caddisflies, stoneflies, midges, and other invertebrates.
There is a long list of expert hatch-matchers/authors who have contributed thorough works on mayflies, but there are few resources that teach you how to become a hatch-matcher. Art Flick’s well-known Streamside Guide is a valuable resource from an insightful angler, but Flick shares more of his observations of the trout and mayfly relationship than the method he used to determine what insects inhabit a particular stream. Nevertheless, Streamside Guide is a must-read for all anglers. Al Caucci’s and Bob Nastasi’s onstream Instant Mayfly Identification Guide addresses the how.
Caucci and Nastasi are well known for their books Hatches and the updated Hatches II, which detail the fishable hatches across the U.S. The books display a lifetime of work onstream and have color photos of each insect stage. Flick said Hatches “should be the last word on the subject.” Once you find a mayfly, Hatches II is one resource that will help you understand the particular species, how that species relates to trout, and how to fish imitations of it.
To determine what mayflies inhabit your stream, you need a streamside system that includes a packable reference and tools. The small (41/2″ x 7″), spiral-bound Instant Mayfly Identification Guide takes you through a simple step-by-step process, from gathering an insect to identifying the species. From there, you can go home and read more.
The purpose of Caucci and Nastasi’s guide is to increase your onstream knowledge so you can catch selective trout, not to overwhelm you with entomology. After you learn what insects inhabit your stream, then you can make good use of the many books written on the hatches.
Matching the hatch is just part of the puzzle. After you learn what is in your stream, you must observe the behavior of both the insect and the trout throughout the season. This will take time, and books can help. You must also be able to determine what insect stage the trout are eating—nymph, emerger, adult (dun), or spinner (see illustration above).
When you have it all together, you can answer the question, “What are they taking?” with confidence and select the proper pattern and make the right presentation.
What You Need
Besides the Identification Guide, you’ll need some of the following tools to gather mayflies and to record data. Most of these tools are available at good fly shops.
A few companies package most of the tools in kits (example: J.W. Outfitters, $75) that include a compact carrying case. Caucci also sells many of the products, and of course you can assemble your own kit.
1. Nets. You’ll need a kick net for gathering nymphs from the stream bottom. You can make this by stapling window-screen material to two wooden dowels (broom handles work), or you can buy one. A kick net works best when two anglers use it together. One kicks up the river bottom, the other stands down-
current and catches bugs with the net. In a pinch, you can hold it yourself and perform a minikick, or shuffle.
For gathering emergers, adults, or spinners from the surface or a foot or so under, you’ll need a dip net or a small seine that fits over your landing net. Caucci uses a small white tea strainer that he attaches to his vest with a zinger.
For gathering airborne adult mayflies (duns or spinners), a common butterfly net is a good choice.
2. Observation Container. Once you gather a nymph, you’ll need something to hold it while you make observations. Caucci uses a white plastic cap from a pill bottle or a small white dish, filled with a few drops of water, to hold the nymph. The white background provides good contrast when viewing the bugs.
3. Magnifier. The identification process requires a close, magnified look at an insect. An 8X loop (found in camera shops) that allows some light in through the side works well, though other inexpensive magnifying glasses also work. Expect to spend from $3 to $15. There’s also the Bug View ($12.95;  487-7535) that allows you to view insects/flies from two different angles, top and bottom.
4. Ruler. A small (15-millimeter, about 6 inches) plastic metric ruler makes it easy to measure naturals. Many insect reference books give measurements in millimeters rather than inches.
5. Stream Thermometer. A recording of the water temperature during your research will help you learn about insect emergence timing. Over the years, you’ll become able to predict roughly when hatches occur on your home streams.
6. Notebook and Pen. You’ll want to record your findings—insect characteristics, date, water temperature, weather conditions, fly patterns, fishing results, etc.
7. Glass Vials. They are not a necessity in the insect-identification game, but they make it easy to store insects if you want to take them to your tying bench. You’ll need a solution, like formaldehyde or alcohol, if you plan to store the insects for more than a few days.
Instant Mayfly Identification Guide Process
Use the Identification Guide to identify mayfly nymphs, duns, and spinners. Here’s an example of how to use it to identify a nymph gathered from the stream bottom. Note: The illustrations and chart shown here appear in the Identification Guide, but have been layed out differently to fit into the magazine’s format.
The nymph belongs to Group I, because the length from the head to the end of the wingpad (X to Y) is longer than (or equal to) the length from the end of the wingpad to the end of the abdomen (Y to Z).
Step 2. The next step breaks down the Group I category into Type A or Type B—Crawlers or Clingers. The width of the nymph’s head (W and Y) is wider than (or equal to) the abdomen (X and Z), so it is a Type B, Clinger.
Step 3. In this step, you match the nymph to the appropriate genus. You must eliminate B-1 before you go to B-2, etc. The book shows six genus categories, though we’ve shown just a few. The nymph falls into the B-1 category, because it has two tails and the body size is within 8-12 mm. Genus: Epeorus.
Step 4. The last step determines the species, in this case, of the genus Eperous. The species section includes notes on regions, insect stages, habitat, and a list of the most important species. Again, we’ve shown just a few and there are also descriptions of the duns and spinners that we have excluded for this exercise.
Determine the species by matching emergence dates, distribution, and body size. Then look up the species in the book’s color plates. There are a few Epeorus species to choose from: pleuralis or vitrea. The nymph (shown on page 18) is clearly a pleuralis. Then look for the picture of the adult (below) and the spinner.
Finally, look up the common name in the back of the book. Epeorus pleuralis is listed as “Quill Gordon, Iron Quill.”
Congratulations! You’ve identified the nymph and can now match the hatch with a specific fly pattern. You’re a hatch-matcher.
For a copy of the Instant Mayfly Identification Guide, visit the Virtual Flyshop’s Mayfly Hatch Guide, www.flyshop.com/bench/ hatchguide, or Al Caucci’s Delaware River Club site, www.mayfly.com, where you can also purchase some of the tools needed for identifying mayflies.
Caucci hosts basic and advanced seminars at the Delaware River Club, where he teaches on-the-river bug identification and match-the-hatch fishing techniques.
Ben Ardito is associate editor of Fly Fisherman magazine.