There is a creature that thrives in aquatic vegetation that trout love to eat. It is not a dun or nymph. It is not a pupa or larva. It is not a spider or strider. It is not a fish or fry. It is not a hellgrammite or night crawler. It is not a crayfish or freshwater shrimp. However, it is a close relative of the crayfish. This creature is a scud!
There are ninety species of Gammarus or scud in or North America. Gammarus are important to fly fishers because they live in shallow water no deeper than twelve feet and in most cases in only hip-deep water. In the right habitats with heavy aquatic vegetation, they can provide up to twenty percent of a trout’s diet. Trout that have scud available in their diet may gain an additional pound per year. The presence of scud means that trout are likely to be on average larger than normal. Scud are found in abundance in higher pH waters such as spring creeks, tailraces and streams that capture nutrient run-off. In all cases, the aquatic vegetation is the key habitat.
Some fly fishers call scud a freshwater shrimp but this is not correct. A shrimp has three distinct body sections and its legs are all near the head with none in the tail section. A scud has fourteen sets of legs across the entire body. If you pick up a live shrimp, it will tend to spring out of your hand. If you pick up a live scud, it will tend to curl thus the logic behind using a curved hook. If a scud is drifting in a current, it may tend to curl if not actively trying to swim, otherwise, a scud observed swimming or clinging tend to be rather straight. So, scud fly patterns do not necessarily need to be tied on curved hooks.
Scud swim, they eat, they swim, they breed, they swim, they get eaten by trout. Scud are 100% aquatic, underwater always. Scud cling aquatic vegetation and to breakwalls as the rocks can provide hiding places, and the plant growth around the breakwalls, provides food to the scud. All Amphipods, not just Gammarus or scud love to eat foods available on plants so the plant growth keeps them near the breakwalls.
Adult scud can lay five or six batches of eggs per year producing over 15,000 eggs. The young scud molt about ten times then become adults that continue to molt. In other words, newly hatched scud are miniature versions of adult scud. Scuds range from size 12 to size 22. If you must, only tie one size, then size 16 will generally get the job done.
Prominent colors are gray, tan, green, yellow, cream and orange. The natural gray, tan and green shrimp are of various species in their adolescent and younger stage. As scud age, they tend to turn yellow and at post mortem, cream colored. Knowing this helps in sizing. Tie size 22, size 20 and size 18 in gray, tan or green. Tie size 12 in yellow. A scud may die at any age; thus, cream may be used from Size 12 to Size 22.
Orange or a band of orange are also variations for scud fly patterns. These color variations are important due a parasite Pomphorhynchus laevis that lives in the intestinal tract of a scud and turns part of the scud orange thus forming an orange band. The parasite uses the scud as a carrier to ultimately get into the intestinal tract of a fish where it completes its life-cycle, while all along feeding off both carriers. If a scud dies with the parasite, the entire scud turns orange in color. Scud that die without the parasite turn cream in color.
Another color variation is a scud fly pattern with a distinct orange spot or “hot spot” which imitates an egg bearing scud. Scud mate from late spring, when the water warms up, through to the late summer or early fall, when the water cools. The fall is the ideal time to fish the egg bearing scud as the vegetation dies down and the “hot spot” is very visible. In general, scud are active year-round. However, with more choices to imitate in the warmer months, scud fly patterns are a good choice during winter fly fishing.
Scud do not like bright lights, thus in general, a scud fly pattern is more effective during times of low light around dawn and dusk and during overcast days. Otherwise, scud fly patterns must be heavy enough to get down near bottom where scud hide away from any intense daylight. Scud are good swimmers, but they swim in short bursts of speed and in an erratic almost sideways manner. Your retrieve should be somewhat jerky and ready for a soft take.
Fly of the Month 2.17
- Tom Adams, Alen Baker