This article is an overview of fly fishing flies, and mostly fly fishing flies used primarily for trout. Although we will touch on other species as well. When you browse a fly shop, a catalog or an online fly shop, you will see flies organized into a few broad categories. And then perhaps sub-divided again into smaller categories. But lets us first look at these broad categories. Generally you will see Nymphs, Dry Flies, Streamers and nowadays probably Beadhead Nymphs or just Beadheads. First off all these are common trout flies, and many can be used for other species as well, streamers are especially useful for virtually all game fish.
Nymphs-are flies used below the surface of the water, fish consume anywhere from 70-90% of their diet underwater, so nymphs tend to be the most common type of fly used. Most of the time nymphs are used in conjunction with weight placed somewhere from 1-3 feet up the tippet (leader) from the fly. This way the nymph will sink under the water to where an eagerly awaiting fish will oblige your desire and chomp it. And really that is all you ever need to know to fly fish like a master. OK there is a little more to it than that. Popular nymphs include: Hare's Ear, Pheasant Tail, Prince Nymphs, Stonefly nymphs, and Copper Johns.
Beadheads- Beadheads or beadhead nymphs migrated to America from Europe and became wildly popular. (Well not the actual nymphs, but the fly patterns.) Unfortunately fish are not stupid, and while they are still the most popular category of pattern today, they are not the panacea we all though twenty years ago. Yes, fish do evolve. Beadheads are simply nymphs with a little, usually gold bead, by the eye of the hook. They allow faster sinking, a different 'swimming action', and the bright bead attracts fish. Popular beadheads include all the nymphs named above with a beadhead tied in front of them.
Dry Flies--Dry Flies are the classic fly requiring the graceful casting that most non-fly fishers think of as fly fishing. Dry flies are tied to float on top of the water, and provide for remarkable strikes from fish as they rise to the surface eagerly attack your offering. While being the most dramatic form of fly fishing it also requires the most stealth and patience and can cause the most frustration. But the rewards are exhilarating. Popular dry flies include: Adams, Elk Hair Caddis, Stimulator, Wulffs, Parachutes.
Streamers-Streamers are 'flies' or patterns tied to imitate smaller fish, leeches, and crustaceans. To think that fish only eat insects is foolish snobbery, although a thought maintained by some. Fish eat indiscriminately, and that includes everything available to them, even the bit of your sandwich that fell into the water. There are times and places where minnows and leeches make up the majority of a game fish diet, and unlike many nymphs and dry flies, streamer type food is available year around. Popular streamers include Woolly Bugger, Muddler Minnows, Egg-Sucking Leech, Mickey Finns. Many of these patterns are available either as a beadhead or the similar conehead.
These categories can be broken down again, and even again. Dry flies in particular have a wide variety of sub-categories, including parachutes, which is taking standard dry flies and tying the hackle in a different fashion. You can also throw in a terrestrial category which is nothing more than a dry fly, whose origin was not the water. Such as ants, hoppers or beetles.
There are also specialty flies and these are generally classified by fish species instead of fly type. The exception is egg flies, which just look like fish eggs and while they are widely used for salmon and or steelhead they are also popular for trout. Besides salmon/steelhead flies, there are also bass flies which are also used for pike and other fish. And saltwater flies, which once again can be broken down further into species. As these are highly specialized, the fly angler interested in them probably already has an extensive knowledge for their area, if not they should consult an guide or fly shop in their local vicinity.