As a teenager, my box of go-to winter trout flies consisted of exactly two patterns: pink San Juan worms and orange salmon eggs. I was caught up in the misconception—as are many anglers, I think—that when the water's freezing cold, there are no bugs hatching, so I'd better drift something colorful that will look to a sluggish trout like an easy-to-get, protein-rich meal. I realized I was wrong one sunny afternoon in January as I sat on the bank of New Jersey's Pequest River, where thousands of tiny black stoneflies were crawling on the snow. I wasn't carrying a nymph box, but I managed to dig an ant pattern out of the bottom of my pack. I sunk it, swung it downstream to a riffle, and tied into a small rainbow trout within five sweeps of the run.