Crustacean · Gammarus and Asellus
Scud and Sowbug
Also called Freshwater shrimp, Cressbug, Gammarus.
Short answer
Scuds and sowbugs are small freshwater crustaceans that live year-round in weedy spring creeks and tailwaters. They do not hatch, so trout eat them every day of the year, and on rivers like the Bighorn and the Green they can make up the majority of a trout's diet. Hook sizes 12 to 18.
What a scud and sowbug is
Scuds and sowbugs are crustaceans rather than insects, and that single fact is why they matter so much. They have no emergence, no season and no life cycle an angler needs to track — they simply live in the weed beds all year and get dislodged into the current, which means a trout in a weedy tailwater is eating them every day of its life. Scuds are laterally flattened and swim in short darts; sowbugs are flattened top to bottom and crawl. Both are grey, olive, tan or pinkish-orange, and the orange ones are usually dead or dying, which is why a pink scud works so well.
- Hook size
- Hook sizes 12 to 18
- Colour
- Olive, grey and tan alive; pink to orange when dead or egg-laden
The stages trout eat
- Scud
- Curls when at rest, straightens when swimming. Fish a straighter profile than most patterns suggest.
- Sowbug
- Flat, grey and slower. The staple food of the Arkansas and Missouri tailwaters.
- Dead or dying
- Turns orange-pink. A pink scud is not an attractor — it imitates a real, very edible thing.
When does the scud and sowbug hatch?
| When | What is happening |
|---|---|
| All year | There is no season. Scuds and sowbugs are available every day on the waters that hold them. |
| Winter | Most important, because almost nothing else is hatching and trout still need to eat. |
| After high water | A rise in flow tears weed apart and washes crustaceans loose. The best scud fishing of all. |
Emergence dates move with latitude, altitude and the weather of a given year. Treat these windows as a shape, not a diary, and check a local report before you travel.
Where it matters
Weedy tailwaters and spring creeks: the Bighorn, the Green below Flaming Gorge, the San Juan, the White and Norfork in Arkansas, Lake Taneycomo, the Pennsylvania limestone creeks, and the Driftless spring creeks of Wisconsin, Minnesota and Iowa.
Fly fishing in Arkansas Fly fishing in Utah Fly fishing in Montana Fly fishing in New Mexico Fly fishing in Wisconsin
How to fish it
Dead drift it deep, close to the bottom and close to the weed. This is nymphing without a hatch to time, so the variables are depth and drift rather than timing. Fish it immediately after a flow increase if you can — a rising tailwater dislodges crustaceans by the thousand and the trout know it. On spring creeks, a scud drifted along the edge of a weed bed is the most reliable fly in the box.
- Fish it straight, not curled. A curled scud is a resting one, and trout eat the swimming ones.
- Orange and pink are realistic, not gaudy. That is the colour of a dead scud.
- The hours after a flow increase are the best scud fishing you will get.
Flies that imitate it
Each of these is a card in the deck, and each has a full page in Our Fly-brary.
Keep reading
- Dry fly vs nymph — which stage to fish, and when
- Why trout refuse your fly — usually the wrong stage, not the wrong pattern
- Best time of day to fly fish — the daily logic behind the table above
- Our Fly-brary — every fly in the deck, explained