Catgut Biothread is one of the best materials for tying extra effective, super-realistic nymphs. Its very unique characteristics and versatility make it a top choice among the world’s most experienced fly tyers. This material is opaque, solid-colored when dry, and becomes milky translucent and shiny when wet. When submerged in water, it also becomes very soft, flexible, and stretchable, which makes it super easy to work with. As it soaks in water, its volume also increases, giving a plump appearance to the fly. The most amazing benefit of using this material is the way it looks in water – flies tied with it look extremely authentic, have lifelike texture, and super-high shine. The material has been treated to extend its durability underwater.
To apply, soak the part you want to use in warm water for 3-5 minutes prior to tying. The color will change from opaque to more milky and transparent and the material will be super-flexible and easy to wrap. When the fly dries, the body will go back to its solid-colored state. By using various colored threads underneath it for the underbody, different effects can be achieved as the color peaks through the wet material. The combinations are really limitless. See below for detailed instructions.
Catgut Biothread is about 50 cm long (about 20”), comes in four diameters, and wide range of colors.
Sizes (Diameters) and hook recommendations:
- Extra Small (0.18mm) – for hooks #16 and #20
- Small (0.3mm) – for hooks #14 and #16
- Medium (0.5mm) – for hooks #12 and #14
- Large (0.7mm) – for hooks #8 and #10
Catgut Biothread is perfect for making bodies for nymphs and emerger flies. It is also a great choice material for making loops on traditional salmon flies (small diameters, in particular, XS and S)
How to use Catgut Biothread
Tying a Classic Micro Nymph with Catgut Biothread
TYING A CLASSIC MICRO NYMPH
with Catgut Biothread
Prior to tying, soak the part of Catgut Biothread that you want to use in warm water for 3-5 minutes. The color will change from opaque to more milky and transparent and the material will be super-flexible and easy to wrap. When the fly dries, the body will go back to its solid-colored state.
Finished Micro Nymph with dry body
Micro Nymph after a few seconds of soaking in water
By using various colored threads for underbody, different effects can be achieved as the color peaks through the wet material. The combinations are really limitless.
Micro Nymph with green underbody thread
Micro Nymph with green underbody thread - soaked
Micro Nymph with brown underbody thread
Micro Nymph with brown underbody thread - soaked
Fly Tying a Catgut Caddis Pupa
For a full list of ingredients for this recipe, go here.