Entomology—the study of the bugs, learning their Latin names and being able to identify them through recognition of their key characteristics and peripheral parts—will add some adventure to your fishing, if you have a mindset that's interested in such things (clearly Rick and I do).  It will also add some trout to your catch, because the more you know about the world in which trout swim, and the things that trout make a living eating, the more of them you'll be able to coax to cunningly disguised hooks.  

But as a start, while you begin to aquire that knowledge about mayflies, or as an end if you have no interest in entomology, or luckily don't have to spend as much time on trout water as poor Rick and I are forced to do, you can let that study slide and pare your imitations of mayflies down to a simple set of flies that will fit in one fly box.  I recommend here at the onset of this article that you buy such a box, and dedicate it solely to mayfly imitations.  That box should be of medium size, though if you buy a large one, and leave expansion gaps, I promise you'll have no trouble filling it up as you encounter mayfly hatches over the next season or two.  It should be designed to hold both sunk flies—nymphs and wets—and dries. 

Starting with nymphs, in the mayfly order, they're broken down into swimmers, crawlers, clingers and burrowers, based on the way they move in their habitat down on or near the bottom.  You don't need specific imitations for all of them, though it won't hurt your chances if you carry something that looks at least a little like each of them.  Trout eat a lot of all the different sorts of them. 

The most important swimmers are the small to tiny Baetis, nymphs of the blue-winged olive group.  They're typically brown to olive-brown, and range from size 16 down to 22.  The Pheasant Tail nymph is standard for them; I use it in the PT Flashback version, and recommend you tie or buy them in that range of sizes, and make that the first row of flies in your dedicated fly box.  Extend that row of PT Flashbacks into size 12 and 14, and the same fly will fish for the closely-related stillwater Callibaetis, or speckle-wing nymphs.  Trout feed on Baetis and Callibaetis nymphs selectively often enough that you need to imitate them frequently.

Crawler nymphs, immatures of the various larger and lesser green drakes (Drunella) and the famous pale morning duns (Ephemerella), are less often taken selectively, but they're very often fed on as part of the drift, day in and day out, hour by hour.  Trout know what they look like, and know what to do about it when they see one coming down the current.  You'll be making a mistake if you don't have a row of something that looks a lot like them in your fly box.  To me, that something takes two forms.  The first is the great Dave Whitlock's Fox Squirrel Nymph, tied a bit portly in sizes 12 to 16.  The second is the Beadhead Hare's Ear, tied in the same narrow range of sizes.  Tumble either of these near the bottom in the kind of cobbled and broken water that crawlers prefer, and you're very likely to be in business whether trout are selective to the naturals or not.

Clinger mayfly nymphs, such as those of pale evening duns (Heptagenia) hold so tightly to bottom rocks that they're not common in the drift.  They normally migrate out of that brisk habitat, to softer water along its edges, before the duns risk emergence.  The same two flies listed above for crawlers are all I feel it's necessary to carry in order to cover them as well as need be.  I don't tie nymphs specifically for clingers. 

Burrower nymphs, such as the Hex (Hexagenia) and brown drake (Ephemera), are both large and long, and own plume-like tails and gills.  I carry nothing more than a row of size 8 and 10 Brown Woolly Buggers to imitate them on the rare times when I get into them.

It's no accident that all of the flies listed for mayfly nymphs are also excellent searching patterns.  The reasons come down to one of those chicken-or-egg questions:  Are they great searching flies because they look like so many mayfly nymphs, or do they work when mayfly nymphs are active because they're such good universal flies?  I'm not sure which it is, but I'm sure they work when trout are selective to mayfly nymphs and also when they're not, so they're all important patterns to carry.

Mayfly emergers and duns both come in a repeated set of color themes, and it's best to focus on these themes, rather than Latin names and identification to genus and species, when you're selecting flies for that initial fly box.  Because almost all emergers and duns arrive in nearly the same shape, despite wide variations in size and narrow variations in color, you can select a small set of patterns for different water types, then tie them in the correct sizes for each color theme, and have almost the entire range of mayfly hatches covered; almost—the exceptions are not the subject of this minor note, but they're what those expansion gaps in your new fly box are for. 

The four repeated themes are roughly olives, sulfur/pale morning/pale evening duns, mahagony/march browns, and blue duns.  If you tie the same small set of flies in each of those themes, you'll find few mayfly hatches that you're unable to match. 

Selecting a set of imitations, or pattern styles, for the themes is not as difficult as it might seem.  You need to start with one emerger style that floats flush in the surface film, imitating the nymph that has just arrived at the top and is beginning to split the nymphal exoskeleton and release the wings of the dun.  This can be a Foam-ball Emerger or a CDC Floating Nymph/Emerger in the famous Rene' Harrop's style.  See Rene's fine new book Trout Hunter (Pruett, 2004) for all the details.  Then you need a style that imitates the dun more fully emerged, but with the nymphal shuck still trailing.  One of the best styles is Craig Mathews's Sparkle Dun; another is the justly famous Quigley Cripple style, originated by Bob Quigley. 

For duns, its best to carry two or three styles for each color theme, each of the styles designed to work best on a different water type, from brisk to smooth.  Appropriate styles range from the fragile Swisher and Richard's No-hackle through the more durable Caucci and Nastasi Compara-dun to the hackled and high-floating standard Catskill tie.  If I'm tying to fill my own fly box, my dun styles will include Parachute Duns, Rene' Harrop's Hairwing Dun, and Shane Stalcup's CDC Biot Comparadun (see Shane's Mayflies: Top to Bottom (Frank Amato, 2002).  I'm also a fan of the wonderful A. K. Best, his mayfly style, the Biot Dun, and his books (I highly recommend A.K's Fly Box, Lyons & Burford, 1996).  Those styles cover all types of water, and give me very different styles to show trout when they get picky.  Often that pickiness seems to be at whim, without reason, and the only way to find the correct fly style is to show them each, one at a time, until the right one is happened upon. 

It's critical to tie or buy your chosen dun and emerger styles in the right sizes for each of the four repeated color themes.  The olives range from tiny size 22s up to the green drakes, in size 10 and 12.  The sulfurs range from size 20 PMDs up to size 12 PEDs.  The mahagonies have a narrow range from size 12 to 18.  Blue duns are typically small, size 16 and 18. 

Spinners of most mayfly species get condensed into just a couple of color themes:  red quills and blue quills.  You can choose your own favorite pattern style, or better yet a couple of them, from Hen-Winged, Polypro, and CDC biot styles.  It's always best if the bodies of your spinner dressings are wound from either dyed hackle stems or dyed biots.  Both give a very slender and segmented effect. 

Tie your Red Quill Spinners in sizes 12 down to 20.  Tie your Blue Quill Spinners from size 16 to 20.  With that small range of sizes, in that truncated couple of colors, you'll be able to solve nearly all mayfly spinner falls, all across the continent, and in fact all around the world.

That completes a condensed list of flies that match most mayfly hatches.  It will provide you a good winter's tying, or a satisfactory burst of buying if you don't tie.  The gaps that remain in your box, if you've bought one sufficiently big, will be filled with imitations of such things as tiny Tricos (Tricorythodes), that are very important when you encounter them, but don't quite fit the confines of this repeated-themes concept. 

It's a rule that the most important insect in the world is the one in front of you when trout are feeding selectively.  Most of the time this list of flies will solve that situation if the offending bug is a mayfly in any of its stages:  nymph, emerger, dun, or spinner.  When it's not, you're thrown back on your own observations and innovations, which is not a bad place to be when you start. 

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