The Biot Rock Worm – Beginner Fly Lesson #9 (Vault Rework)

There’s nothing flashy about the Biot Rock Worm — and that’s exactly the point.

This pattern was born straight from the stream. I sampled rocks, checked drift, and even peeked at trout stomach contents. What I found over and over again were tiny green rock worms crawling around the streambed — no wings, no shimmer, just movement and shape.

So I tied a fly to match them.

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🧪 A Quick Look at the Rock Worm

"Rock worm" is the nickname often given to the caddisfly larva stage before it builds a case. These critters crawl freely across the bottom of freestone streams, living a quiet, well-fed life until it’s time to pupate.

In early stages, they’re often bright green — almost chartreuse. But right before metamorphosis, they start to darken near the head. That’s why I tie two versions:

• 💚 Winter: All green

• 🖤 Spring/Summer: With a black or brown biot shell on top to mimic that darkening

They’re easy to miss — but trout don’t ignore them. In fact, when caddisflies are active, rock worms are usually part of the story. This fly fishes great during caddis-heavy periods, especially before or between hatches when trout are keying on movement near the bottom.

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🪶 Materials & Notes:

• Hook: Daiichi 1270 #12–14

• Thread: MFC 8/0 Light Brown

• Tail: Tan marabou

• Underbody: Your choice of dubbing

• Rear body: Turkey biot dyed caddis green

• Rib: Green ice thread

• Legs: Dark partridge

• Front body: Chartreuse dubbing

• Front shell: Turkey biot dyed caddis green

🧠 Pro Tip: A bright green Sharpie is essential for getting the right tone. Don’t skip it.

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🎣 Fishing Tips:

Great for euro style and high sticking 

Drag it along the bottom.
Yes, you’ll lose some. But that’s where the fish are feeding.
I fish these low and slow, in fast water or soft pockets — and when I feel that thunk, I know it worked.

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🎥 Biot Rock Worm – Beginner Fly Tying Lesson #9 (Vault Rework)
📺 https://youtu.be/UxVcjBGZHc0

This isn’t just another green bug — it’s a field-tested, trout-approved pattern designed by Johnny Utah to match the real rock worms crawling your home waters.
Fast to tie. Rugged to fish. And perfect for beginner tyers learning how to bring that subtle realism to life.

Tied from the stream, tested on the trout,
the Biot Rock Worm crawls its way into fly box legend.
Keep it low… and let it wiggle.
– Johnny Utah