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The Scud is one of our all time favorite nymphing flies. It was on a small stream in our local town that we saw it in action. Us kids were fishing with dry flies and the old man was using a Scud, needless to say, he was the one who caught fish during that foray. The Scud was also the fly that caught our first fish on a fly that we tied ourselves. In other words, the Scud is a killer fly for us here at Currant Creek Fly Co.
Gammarus is the traditional scud and can be found throughout the entirety of the Northern Hemisphere, while the Hyalella are found primarily throughout the American continents. While species in the Gammarus genus can be found in various water conditions, from saltwater to fresh. Hyalella are found mainly in freshwater. Between these two genus’ of amphipoda there are hundreds of scuds. The most common species in North America is in the family hyalella, the Hyalella azteca, and can be found in a wide distribution area and across many different water types and conditions. While taxonomically there are differences between the multitude of species of scuds, for the fly-fisherman, there really are not many differences that we should be aware of.
Scuds can be found in most water systems that are fished, from freestone spring creeks, tailwater rivers, and most stillwaters. The H. azteca can be found in alkaline and brackish waters, and even some levels of acidity, no less than a pH of 6. Scuds are generally light sensitive, most of their activity is done during the low light conditions of the morning or evening. They are also quite active during an overcast day.
They are a primary food source for many different creatures, from the fish that inhabit the streams to the waterfowl. In fact it was discovered that 97% of the diet of female White-Winged Scoters and a significant part of the diet of the Lesser Scaup is scuds. Because of their role as a major food source for many animals, the Spiny-Headed Worm, a simple parasite, uses the Scud as an intermediary carrier.
This parasite is reddish in nature, and due to the opaque nature of the scud, appears as a red spot in the Scud. As well, the parasite snatches brain function away from the scud host and makes it behave erratically, compared to its normal behavior. For example, scuds typically avoid the light, when infected by the Spiny-Headed Worm scuds are known to swim around in the light and even swim to the surface. Biologist believe that this snatching of brain function allows the parasite to increase its ability to get to its primary hosts, such as ducks. This erratic behavior also increases the predation of scuds by fish in the environment.
The life cycle of the scud is fairly simple. As with any crustacean, the scud is required to molt its exoskeleton as it grows. The common scud has roughly 15-20 instars, or molting phases. At instar 6 gender can be determined, mating begins during the 8th, and the remainder instars are known as the adult phase. These scuds live for roughly a year, during which time they will have 3-4 broods, of about 50 eggs each. In other words, the scud is the rabbit of the waterways. During mating, the female will “lay” her eggs in a marsupium pouch which the male then fertilizes. These eggs tend to take on an orange hue, which once again makes a pregnant female scud a little bit more easily found (a poor evolutionary trait in our opinion).
The most productive time to fish with a scud is during the low-light hours right around dawn and sunset. However, if you have a scud with an orange spot it can be used with success during the bright hours of the day. Scuds are mobile swimmers and are a great fly to begin nymphing with because they don’t have to be bouncing off of, or close to, the bottom of the waterway like most other nymphs, also the drift of the fly doesn’t have to be completely drag free since a live scud may swim against or faster than the current its found in. Because of the prolific rate of procreation, the scud is an abundant food source that can found throughout many water systems and should be found in every fly-fisherman’s flybox.
Douglas Grant Smith (2001). "Amphipoda". Pennak's freshwater invertebrates of the United States: Porifera to Crustacea (4th ed.). John Wiley and Sons. pp. 569–584.ISBN 978-0-471-35837-4.
Gary L. Krapu & Kenneth J. Reinecke (1992). "Foraging ecology and nutrition".Ecology and Management of Breeding Waterfowl. University of Minnesota Press. pp. 1–29. ISBN 978-0-8166-2001-2.
"Aquatic Invertebrates: Amphipods". The Nature of the Rideau River.Canadian Museum of Nature. May 18, 2007. Retrieved May 13th, 2014.