Scuds (Gammarus)
Gammarus lacustris · Aquatic life
Whole animal · Photo: Erin McKittrick / CC BY
Also called Gammarus lacustris, Side swimmers, Amphipods, Freshwater shrimp
How to identify Scuds (Gammarus)
- Shrimplike, up to about 3/4 inch
- Body flattened side to side, gray green to olive or tan
- Swim on their side with quick darts
- Tufts of spines on the upper tail segments
- Turn orange or red when cooked or dead
Similar species
Hyalella scuds are smaller, under about 1/3 inch, and smoother. Opossum shrimp (Mysis) in a few deep lakes are straighter bodied, swim upright and have stalked eyes.
Profile
| Season | Present all year. |
|---|---|
| Starts | Active even in cold water; breeding peaks in spring and summer |
| Depth | Plant beds and bottom, shallow to moderate depths |
| How it spreads or reproduces | Carried on plants and equipment; sometimes stocked as trout food |
| Habitat | Cold to cool, hard water lakes, reservoirs, ponds and spring fed waters with plants; often very abundant in productive trout lakes. |
Why it matters in a lake
A major reason some lakes grow big, fast trout. They feed on algae and detritus and need good oxygen, so a large scud population is a healthy sign.
Where it is found
- Idaho: Common
- Oregon: Occasional
- Wyoming: Common
Classification
| Kingdom | Animalia |
|---|---|
| Phylum | Arthropoda |
| Class | Malacostraca |
| Order | Amphipoda |
| Family | Gammaridae |
| Scientific name | Gammarus lacustris |
Scuds (Hyalella)
Signal crayfish
Aquatic sow bugs
Virile crayfish
Red swamp crayfish
Rusty crayfish
Fairy shrimp
Tadpole shrimp
Clam shrimp
Pilose crayfishNeed a hand?
Found it in your lake?
Send us a photo and we will identify it and tell you what it means for your lake.
Idaho / Wyoming (208) 501-4531Oregon (541) 280-0596