Dry FliesIron Blue Dun
This Iron Blue Dun combines a dubbed muskrat body with a palmered grey hen hackle and a face hackle of grey partridge, producing the dark, slate-colored silhouette of the natural. A tying-thread butt and grey hen hackle-barb tail round out a sparse dressing for picky trout on technical water.
Spring, Summer, Fall
Intermediate
Trout
Feb 2026
Overview
Hans Weilenmann's dressing leans on muskrat fur for the body's dark, mottled color, then layers a soft grey hen hackle beneath a stiffer grey partridge hackle to combine movement with flotation. The scarlet thread butt is a small but visible tying detail that also helps anchor the tail. It's built for the low-light, overcast conditions the natural favors, when trout hold in slower water and study each fly closely. Fish it dead drift on rivers and stillwaters during spring and fall Baetis-type hatches.
Where to Buy This Fly
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Materials
- Hook:
- Umpqua U203 #14
- Thread:
- Danville Flymaster 6/0, scarlet
- Hackle:
- Partridge, grey
- Body Hackle:
- Hen, grey
- Tail:
- Hen hackle barbs, grey
- Body:
- Muskrat
- Butt:
- Tying thread
Behavior & Presentation
Natural Behavior: Iron Blue mayflies emerge on cold, overcast days, floating motionless for extended periods while their drab wings slowly dry, often trapped in back eddies and slow pools. Their dark blue-grey coloration makes them highly visible against light-colored water surfaces, allowing fish to feed confidently during poor weather hatches when duns remain vulnerable longer.
Where Trout Eat It: Trout feed on dark Baetis niger during overcast cold-weather hatches, targeting duns trapped in UK chalk stream margins.
How to Fish It: Present sparse dark pattern with delicate upstream cast during poor-weather hatches for natural slack-water drift.
Best Water: Fish carrier channels along weed edges, spring creek eddies below weed beds, and slow inside bends where duns become trapped.
Strike Type: Trout take this sparse dark pattern with delicate sipping rises in slack water. Watch for subtle dimples or quiet head-and-tail rises as fish feed methodically during cold-weather hatches, rather than splashy refusals.
Fishing Strategy
Rigging Suggestions: Use a 9-12 foot leader tapering to 5X tippet for delicate presentations. Apply floatant to the body and hackle.
Seasonal Timing: Most effective during peak feeding periods at dawn and dusk. Water temperatures between 45-65°F typically produce best results.
Pro Tips: This classic British pattern remains effective across Europe and North America wherever small dark mayflies hatch. The subtle dark coloration and sparse hackle create an authentic silhouette that fools educated trout.
Entomology
Mayfly duns emerge on cold, overcast days, floating motionless for extended periods while their drab wings slowly dry, often getting caught in back eddies and slow pools. Fish feed confidently on these duns during poor weather hatches because the insects remain vulnerable for longer durations, and their dark coloration makes them highly visible against light-colored water surfaces.
- Order
- Ephemeroptera
- Common Name
- Mayfly
- Organism Type
- insect
- Life Stage
- adult
