Dun
Also called Mayfly dun, Subimago
A dun is the newly emerged, winged subimago stage of a mayfly, right after it leaves the water and before it becomes a spinner.
- Group
- Life stages
- Category
- Entomology & forage
- Level
- Intermediate
- Water
- Freshwater
Last updated
What Dun means
Mayflies leave the water as a winged subimago called a dun. This stage starts at emergence, when the insect rides the surface film or crawls out, then flies to nearby vegetation.
Duns are not fully mature. Mayflies are unique in having this extra winged molt, but in a few species the females skip that second molt. When the molt happens, the time to molt can vary from minutes to days depending on species. That second molt is a mayfly-only detail, caddisflies and stoneflies do not have a dun-to-spinner step.
On the water, “dun” usually points to dry-fly and emerger situations. Patterns like a Comparadun or a parachute are common stand-ins for a mayfly dun, while an emerger covers the moment when the insect is still trapped in the film.
Why it matters on the water
Separating dun from spinner helps narrow the target. Duns tend to show up during the main hatch, with insects drifting, struggling, and taking off. Spinners show up later, often in a tighter window, and sit flatter and more spent.
That choice changes your fly and your approach. A dun look pushes you toward higher-floating dries or emergers and careful drag control in the seam or lane where insects are popping. If the naturals look spent and motionless, switching to a spinner profile usually outperforms changing tippet sizes or moving runs.
Read next
- EmergerA fly that imitates an aquatic insect in the act of emerging, partway between nymph or pupa and a dry fly. It is fished in or just under the surface film, where trout often feed.
- HatchA hatch is a period when aquatic insects emerge in numbers, often bringing trout into a steady feeding rhythm.
- MayflyA mayfly is a freshwater insect with aquatic nymph stages that trout and other fish eat in every stage of its life cycle, from nymph to dun to spinner.
- SpinnerA spinner is a dry fly that imitates an adult mayfly after it has mated and fallen spent on the water, usually with wings laid flat to the sides.