Hook heavy jig hook (Fulling Mill Jig Force / equivalent), 10-14
Thread brown or olive 8/0
Materials
Bead Large slotted tungsten bead (3.8-4.0mm) (1)
Weight Tungsten jig back / lead-free wire under-wrap (as needed)
Case body Coarse dubbing blend of brown, olive and hare's-ear (spiky) (small pinch)
Rib Fine gold or copper wire (1 strand)
Head/thorax Black or dark brown dubbing (small pinch)
Legs/collar Partridge or CDC fibres (sparse) (few fibres)
How to tie it
Slide the slotted tungsten bead onto the jig hook and seat it behind the eye; add a few turns of lead-free wire or a tungsten jig back behind the bead to load extra weight low and forward. This is a purpose-built anchor fly to sink a rig fast.
Start thread behind the bead and lay a smooth base back to the point of the barb.
Tie in the wire rib at the rear, then dub a fat, spiky, tapered caddis-case body forward over the back two-thirds of the shank; keep it rough so fibres stick out like debris.
Counter-wrap the wire rib forward in 4-5 open turns to segment and armour the case, then tie off and helicopter to break.
Dub a small dark thorax/head behind the bead in one or two turns.
Add a sparse collar of partridge or CDC fibres for a hint of legs, whip finish behind the bead, and a drop of varnish.
Pick out the case dubbing with a dubbing brush so it looks scruffy and buggy.