Although the concept of "matching the hatch" has been central to flyfishing for 150 years, it has been used almost exclusively for dry flyfishing. With Common Nymphs of Eastern North America: A Primer for Flyfishers and Flytiers, Caleb Tzilkowski and Jay Stauffer Jr. take trout enthusiasts in another hatch-matching direction--to the year-round underwater nymph "hatch," which, in most cases, constitutes 90 percent of trout diets.

Successful flyfishers have at least rudimentary knowledge of the organisms that artificial flies imitate. The relatively few and very best anglers...