Net Builder Caddis

The Net Builder Caddis is a realistic caddis larva imitation that replicates the free-living, net-spinning caddis species that build silken nets to filter food from the current. This weighted pattern features a Thinskin casing over Sow Scud Dubbing for a translucent, segmented body, a white Z-Lon tail suggesting the anal gills of natural larvae, and ostrich herl legs that create movement and suggest the thoracic legs of natural caddis larvae.

Net Builder Caddis fly pattern - imitates Caddis, Caddis Larvae tied for Trout
  • Intermediate
  • Spring, Summer, Fall
  • Trout
  • Size 10–16

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The Net Builder Caddis is a realistic caddis larva imitation that replicates the free-living, net-spinning caddis species that build silken nets to filter food from the current. This weighted pattern features a Thinskin casing over Sow Scud Dubbing for a translucent, segmented body, a white Z-Lon tail suggesting the anal gills of natural larvae, and ostrich herl legs that create movement and suggest the thoracic legs of natural caddis larvae.

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Materials

Hook
Hanak 300, size #10–#16
Weight
.020 Lead Wire
Thread
Black UNI 8/0
Tail
White Z-Lon
Rib
3X Tippet Material
Casing
Olive Fly Specks Thinskin
Body
Olive Sow Scud Dubbing
Legs
Gray or Black Ostrich Herl

Overview

This Charlie Craven pattern from Charlie's Fly Box represents the often-overlooked net-building caddis larvae that are incredibly abundant in freestone streams. Unlike case-building caddis, net-spinners live in silken retreats attached to rocks where they filter organic matter from the current. The pattern's construction creates a realistic larval profile with the Thinskin casing providing the characteristic translucent appearance of natural caddis larvae. The white Z-Lon tail imitates the distinctive anal gills, while the tippet ribbing creates segmentation and adds durability to the pattern. The lead wire underbody ensures the fly reaches the bottom quickly where natural net-building caddis live.

Related patterns

Behavior & presentation

Natural Behavior
Hydropsychidae larvae abandon their fixed silken nets during high water or when searching for better feeding sites, tumbling along the bottom with their distinctive white anal gills visible. The translucent Thinskin casing over dubbing perfectly captures the see-through quality of these soft-bodied filter feeders.
Where Trout Eat It
Trout intercept net-building caddis larvae in fast riffles and pocket water where the naturals build their silk hunting nets on slick rocks. Fish position in feeding lanes just downstream of rocky riffle edges where dislodged larvae tumble.
How to Fish It
Dead drift near bottom using weighted rigs or euro setup. Cast up and across into rough pocket water, maintaining tight line contact. Let fly swing downstream at drift end, as larvae naturally tumble and swing in current.
Best Water
Focus on fast riffles with slick, algae-covered rocks and pocket water where net-spinners construct silk retreats. Target transition zones where riffles spill into runs, and seams along boulder edges.
Strike Type
Weighted nymph takes feel like hesitations or taps transmitted through the tight line; set with a swift lift while maintaining tension throughout the drift.

Fishing strategy

Rigging Suggestions
Fish on a standard nymphing rig or euro nymphing setup with a tight line. Works well as a point fly in a two-nymph rig or as a dropper behind a larger attractor pattern. Use 5X-6X fluorocarbon tippet.
Seasonal Timing
Most effective from when caddis larvae are actively feeding and growing. Particularly productive during periods of high water when dislodged larvae are available to trout.
Pro Tips
This is a subsurface pattern designed to sink quickly and drift near the bottom. The olive coloration blends with natural stream substrates while the ostrich herl legs provide subtle movement that attracts attention.
From River & Run

Where to fish it

Rivers anglers pair with this fly, with local shops that stock it.

Open River & Run

River details and fly shops from River & Run, our sister site.

Entomology

Caddis larvae construct fixed net structures on rocks to filter food particles from the current, but they occasionally abandon these retreats and drift downstream seeking new territory. Fish capitalize on these displaced larvae because they're soft-bodied and unable to escape once swept into the current.

Order
Trichoptera
Common name
Caddisfly
Organism
insect
Life stage
larva

Pattern details

  • Moving Water
  • Rocky Mountain
  • dead-drift
  • indicator-nymph
  • caddis-hatch
  • attractor
  • searching-pattern
  • high-water
  • freestone

Get this fly

Net Builder Caddis, tied and ready to fish

Hook #10 to #16 · Intermediate