My good friend James Marsh has recently reminded me of a few things about matching the hatch. "Matching the Hatch" is a very popular term used by anglers. However, it’s only correct during the time an insect is hatching, which on the average, is less than 5 percent of the total number of days any species of aquatic insect lives. For example, a mayfly that lives a year, usually only hatches during a period of a week to three weeks in any one given stream, although this varies greatly from stream to stream and species to species. The majority of its life is spent as a nymph!
What you need to match isn't just the hatch. It's the insect’s entire life (from the time it changes from an egg to the larvae stage of life, which in the case of a mayfly, is a nymph) until a few hours after it dies. You need to match its death or the insect when it dies on the water depositing eggs for future generations. These spinners, in the case of mayflies, are usually eaten by trout. So keep in mind, when I am referring to matching the foods trout eat, I'm not just referring to "matching the hatch", I'm referring to matching the entire life span of the insect including a short time after it dies.
To learn more about "matching the hatch" check out this free on-line class at Trout University. Class 3021 Matching the Hatch by Stephen Maslar Chancellor at Trout University. Mayflies- Fly Fishing guide to Imitating Aquatic Insects is an important DVD about mayflies including the life cycles. (However, the DVD is not free as we do need to pay some bills.)