Sulphur Dun

Overview: The Sulphur Dun (Ephemerella invaria) is a hallmark mayfly hatch in late spring and early summer, especially in the eastern United States. These iconic insects, with their warm yellow-orange bodies and semi-transparent wings, are a favorite for both trout and anglers. Their predictable emergence during evening hours often triggers intense surface activity, making them a must-have in any fly box.

Nymph Stage: Sulphur nymphs are stout and crawler-like, measuring around 1/4" to 1/2" in size. They range in color from olive-brown to pale yellow, with prominent dark wing cases. Hook sizes 14–16 are most effective for imitating these nymphs. Fish them with dead-drift techniques near the bottom, particularly in riffles and runs, as they migrate to shallower water to emerge. Adding a gentle lift at the end of the drift can mimic their ascent and entice strikes.

Adult Stage: Adult Sulphur Duns are approximately 1/4" to 1/2" long, with yellow to orange-tinted bodies and pale gray, semi-transparent wings. The duns emerge predominantly during the evening, creating prime dry fly fishing opportunities. Dry fly patterns tied on hook sizes 14–16 are ideal. Present imitations delicately in slower pools and near riffle edges to match their natural behavior. Spinners, which often fall just before dusk, can be imitated with rusty orange or brown-bodied patterns to extend fishing into twilight hours.