The river's were I do most of my fly fishing, all have a healthy population of scud.
A scud, often mistakenly referred to as a freshwater-shrimp, is a laterally flattened crustacean. They have seven pairs of legs, the first two are used for grasping. Most scuds live in shallow water, in weed, and silt.
They are excellent swimmers and can be found in highly oxygenated, cold alkaline water such as my local river Touvre. They are a power food for fish, contributing to high growth rates in trout. On the river they can be seen in biblical proportions with just a scoop of a seine net through the weed beds.
On most rivers you can see scud of different sizes, and can believe that all the smaller ones are just immature forms of the larger ones. However I now understand that there are two different species. The bigger of the two comes from the family Gammarus, and run in size from size 10s to size 16s. The other smaller species is called Hyalella azteca, and runs from 18s to, too small for me to tie!?
As chalk streams maintain a fairly constant temperature all year round, these highly proteined energy efficient creatures are always available.
On a recent visit to a local river, the 'Heron' scooped a net full of scud, and some had an orange hue to the front of the body. Many think a scud turns this colour when they die, and it may be true. But in this case on closer examination we saw that all the 'orange bits' were in fact mini scud. Tiny, tiny orange scud, all too small to see without a decent pair of magnifying glasses. The 'Heron' told me that scud carry the young in such a way, for protection in the early days!
I tie my scuds in various weighted forms, light, medium, heavy, and very heavy. In the colours gray, and olive, the dubbing is rabbit hair, with some light bright material added for extra flash.
All have the standard shell back, in clear, olive or gray, ribbed with 6x nylon.
Hooks are Tiemco 2488H or Tiemco 2457 in the larger sizes. The 2457s are a heavy hook in themselves, and take weight well. The 2488Hs are better for the smaller sizes in my view?
Later in the season, resident fish can get a little weary of scud, and this is when the smaller sizes, with a very natural dubbing (as close to the natural as possible) can make all the difference.