Dry FliesZ-Dun BWO
Hans Weilenmann's Z-Dun BWO combines a grey polypropylene shuck-and-wing with a light olive SLF Finesse body, matching the pale olive tones and grey wings typical of Blue-Winged Olive duns. Mottled grey hen barbs form the tail, and a Coq de Leon hen hackle keeps the fly riding low, the way a natural sits after breaking free of its nymphal shuck.
Spring, Summer, Fall
Intermediate
Trout
Feb 2026
Overview
The same polypropylene material forms the wing, shellback, and trailing shuck, a construction shortcut that ties an emerging-to-fully-emerged BWO in one motion instead of tying three separate parts. SLF Finesse dubbing on both abdomen and thorax gives a slim, translucent body that matches the small size 18 profile BWOs are known for. Weilenmann built it for the extended blue-winged olive hatches common on tailwaters and spring creeks in spring and fall, on both moving water and stillwaters.
Where to Buy This Fly
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Materials
- Hook:
- Partridge SUD #18
- Thread:
- Benecchi 12/0, grey
- Tail:
- Hen barbs, mottled grey
- Wing/shellback/shuck:
- Polypropylene, grey
- Abdomen:
- SLF Finesse, light olive
- Rib:
- Tying thread
- Hackle:
- Whiting Coq de Leon hen
- Thorax:
- SLF Finesse, light olive
Behavior & Presentation
Natural Behavior: Blue-winged olive duns drift extended periods in the surface film while wings slowly dry during overcast conditions, their upright posture and vulnerable positioning making them highly visible. Cold-water emergences during drizzly weather prolong drying times, concentrating defenseless duns in productive feeding lanes where selective trout sip methodically.
Where Trout Eat It: Floating in the surface film on smooth tailwater runs and spring creek flats, where BWO duns drift predictably through established feeding lanes during prolonged cold-weather emergences.
How to Fish It: Delicate upstream presentations with perfect drag-free drift, using the low-profile flush-floating design to match natural BWO duns struggling to dry wings during overcast emergence periods.
Best Water: Smooth tailwater runs with glassy surfaces, spring creek flats where selective feeding occurs, and slicks below riffles collecting drifting BWO duns during overcast cold-weather hatches.
Strike Type: Subtle confident sips barely dimpling the surface as selective trout methodically intercept drifting BWO duns with minimal effort during technical feeding periods.
Fishing Strategy
Rigging Suggestions: Employ a 10-14 foot leader tapered to 6X or 7X tippet for technical presentations. Use minimal floatant to maintain the flush-floating profile.
Seasonal Timing: Peak effectiveness from March through May and September through November during Blue-Winged Olive emergences, particularly productive on overcast, drizzly days.
Pro Tips: The Z-lon wing post provides visibility while maintaining a realistic profile. During heavy hatches, focus on feeding lanes and observe rise forms carefully.
Entomology
Blue-winged olive duns emerge during overcast conditions and drift slowly on the surface while their wings dry, unable to fly until fully developed. Fish selectively feed on these mayflies because their prolonged drift time in the surface film makes them predictable and accessible, particularly during the extended hatches that occur in spring and fall on tailwaters and freestone streams.
- Order
- Ephemeroptera
- Common Name
- Mayfly
- Organism Type
- insect
- Life Stage
- adult
