Dry FliesBibio Marci
Hans Weilenmann's Bibio Marci sets a hot orange and black seal's fur thorax against a black seal's fur abdomen, capped with a black foam thorax cover and knotted magpie-leg fibers for movement. A sparkle of pearl Holoshimmer forms the wing, giving the small size 14 fly a flash of light during caddis mating swarms on moving water and stillwater.
Spring, Summer, Fall
Intermediate
Trout
Feb 2026
Overview
Weilenmann split the body into two seal's fur sections, an all-black abdomen and an orange-and-black thorax, echoing the segmented, two-toned look of many natural insects rather than a single flat color. Knotted magpie tail barbs form jointed legs that kick during the drift, and a black foam strip over the thorax adds durability. The pearl Holoshimmer wing catches light without adding bulk on the size 14 hook, useful when repeated surface disturbance keeps trout keyed on small, flashy targets.
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Materials
- Hook:
- Kamasan B175 #14
- Thread:
- Benecchi 12/0, black
- Abdomen:
- Seal's fur, dyed black
- Legs:
- Magpie tail barbs, knotted (or any black feather substitute)
- Wing:
- Gutermann Holoshimmer, pearl
- Thorax cover:
- Foam, black
- Thorax:
- Seal's fur, dyed hot orange; seal's fur, dyed black
Behavior & Presentation
Natural Behavior: Caddis drop to the surface repeatedly during egg-laying aggregations, maintaining sustained activity as individuals deposit eggs before flying off again.
Where Trout Eat It: Fish target egg-laying caddis in runs, along seams, and over riffles where reproductive behavior concentrates during warm periods.
How to Fish It: Dead drift or add twitches to imitate repeated egg-laying touches. Fish through prime water where swarms are visible.
Best Water: Focus on seams collecting egg-layers, riffle edges where caddis concentrate, runs with moderate flow, and tail-outs.
Strike Type: Expect visible rises or aggressive takes as fish key on repeated surface activity.
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: The contrasting red and black body triggers strikes even when no specific hatch is occurring. Fish it as a prospecting pattern along undercut banks.
Entomology
Caddis adults gather in mating aggregations over streams and lakes, with individuals constantly dropping to the surface to deposit eggs before attempting to fly off again. The repetitive nature of these egg-laying flights creates sustained surface activity that maintains fish interest throughout extended periods of reproductive behavior.
- Order
- Trichoptera
- Common Name
- Caddisfly
- Organism Type
- insect
- Life Stage
- adult
