Also called the Glo-Bug, this fly imitates fish roe. Many fly anglers won't use an egg fly because it looks too much like bait. That's a silly reason not to use a fly, though. Egg flies imitate a naturally-occuring food that wild trout, steelhead, and salmon eat with gusto. When salmon spawn in the fall, there are always steelhead and trout just downstream from them, waiting to scarf up loose eggs. And whitefish spawn in winter, providing free meals to trout and an opportunity for fly anglers.
Good color choices are pink, peach, red-orange, and chartreuse. Since the fly needs to be on the bottom, weight is sometimes added in the form of non-toxic eyes; this variation is called an Eggo. Sparkle yarn is sometimes used, and some flies are tied with a white hackle collar that imitates an egg with sperm.
How to Fish
During spawning seasons, dead drift near the bottom with the indicator or tight line presentation. If you see spawning salmon, you can cast so the fly lands just behind them and drifts below the spawning pair. You can bet there are steelhead or trout waiting below the salmon for drifting eggs.