Matching the Hatch good hatch is an exhilarating time for fly fishers. It can cause trout to go into a sort of feeding frenzy, lose much of their normal caution, and rise everywhere—sometimes even right at your feet. One of the toughest challenges you may face during a good hatch is controlling your excitment. You may have to concentrate on keeping your hands steady enough to pick the right fly from your fly box and tie it on your leader. This clinic provides some background on hatches and offers tips on how to fish them. What Is a Hatch? A "hatch" refers to the period of time when aquatic insects are transforming from their nymphal or pupal stages into adult flies. In the days before they are due to hatch, these immature insects will move around. They will drift along the bottom or crawl towards shallow water. When the time is right, they will begin to drift towards the surface of the water en masse. Upon reaching the surface the insects will break through their nymphal or pupal casings, and emerge as adults. This moment of transformation is a very vulnerable time for the insects. And it can cause the resident trout to go crazy. When Do Hatches Occur? Different species of mayflies, caddis flies and stone flies hatch at different times of the year. A hatch guide is a good place to start if you're trying to figure out when hatches will happen on your local streams. Timing of hatches is sometimes hard to pin down, so your best bet is to visit the water frequently and collect information from other anglers. Chatting with other fly fishers is a great way to pool information and figure out the timing of the hatch. Hatches of a particular insect generally last a few hours during the day or evening. However, the overall duration of the insect's hatch can last a couple of days, a couple of weeks and in some cases even longer. For example, the western march brown (mayfly) can hatch daily on some Rocky Mountain streams between 11am and 3pm throughout April and June. Keep in mind that some hatches are more significant than others. The famous ones, like the western salmonfly hatch, usually involve large, nutrition-rich flies. These insects offer so much nutrition and are present in such abundance that they attract very large trout to the surface. Many of these trout may otherwise never be catchable on dry flies, since big trout spend most of their deep in water feeding on baitfish and other subsurface fare. Fishing a Hatch Picking the Fly During a good hatch, the trout may become highly selective. This means that they have become so "keyed in" on the dominant insects that they will ignore other flies that come cross their paths. Your challenge during a hatch is to pick the right fly. In an ideal world, you would only need to grab a natural fly off the water, match its size, shape and color with a fly from your fly box, and start catching fish after fish. In reality, fishing a hatch is not quite that easy. Remember, you'll have to present your fly in a way that tricks the fish into thinking that it's a natural insect. With hundreds of flies on the water, a poorly presented offering is easy for a fish to ignore. Reading the Rises Early in a hatch, you may see a few splashy rises here and there. Usually this means that the trout are feeding on the insects below the surface of the water, just before they hatch. Your best bet at this time is to fish a nymph or emerger pattern beneath the surface. Keep in mind: For most hatches, fish feed primarily on the emerging flies. Yet at a certain point, when enough adult flies are on the surface, the trout will switch over and start gulping the adults from the surface. Spinners After the insects have mated, they die and fall onto the water. This is the last phase of the hatch, known as a spinner fall. When spinners are on the water in enough numbers, trout will become selective to this form of the insect. Make sure to have some "spent wing" spinner patterns in your fly box to effectively fish this part of the hatch. Keep in mind that spinners are often difficult to locate on the water since they are usually flat in the surface film. Timing Your Cast Rising trout may go into a sort of rise rhythm during a good hatch. The conveyor belt of the river brings so many flies directly overhead that trout go into an energy-efficient "gulp mode." In this case, it is possible that a trout will ignore your fly if your cast is not timed just right. Your challenge, when casting to rhythmically rising fish, is to get in sync with the trout and plop your fly in front of it just as it's rising up to take its next swallow. Masking Hatches A masking hatch describes a situation when there are several hatches occurring simultaneously. As the name implies, one of the insects, usually the larger one, "masks" the "real" hatch from the angler. For example, you may see trout rising and lots of large brown mayflies on the water. So naturally you tie on a brown mayfly. After dozens of refusals, you notice a smaller, cream mayfly on the water that the trout are eating. You've been duped by a "masking hatch." Why would a trout choose one fly over another? Trout have evolved some remarkable feeding instincts. In a case like this, it's likely that they have chosen the smaller insect because it provides them with more nutrition for their effort than the larger fly would.Or maybe it just tastes better. Terrestrials "Terrestrial" is a term for a land-based insect, like an ant, grasshopper or beetle. These insects provide excellent nutrition for trout. During high summer when hatches of aquatic insects begin to taper off, grasshoppers and other terrestrials may make up a huge portion of a trout's diet. Although terrestrials are not technically a "hatch", they can trigger a hatch mentality in trout.