Northwest Fly Fishing

By Don Roberts

You can buy a packet of three dozen or more live Gammarus specimens (aka scuds) on eBay for $15, with free shipping. Of course, a quick search online will reveal other sources: aquarium enthusiasts tout scuds as being the optimal food for every species from guppies to bluegills, as well as for tropical species from cichlids on up to bettas (Siamese fighting fish). These small-batch scuds are not sold as an end product, but as a starter kit, the culture for producing an ever-increasing biomass. All it takes is a 32-gallon plastic trash can, clean water, and a few handfuls of leaf litter. Given scuds’ proclivity to procreate—I hesitate to say breed like rabbits, which pale in comparison—scud farms provide an economical, if not eternal, source of high-calorie chow for aquarium fish. The same holds true in the wild.
   Though now steeped in obscurity, the word “scud” is probably Scandinavian in origin: derived from either the Norwegian skudda, to thrust, or the Swedish skudda, to shake or jitter. The Norwegian parlance, of course, explains the NATO code name for the Soviet-era R-11 Scud tactical ballistic missile, while the Swedish nomenclature, suggesting the herky-jerky motion of amphipods, could account for the common-usage name of scuds.
   Aside from aquarium aficionados and astute anglers, most people wouldn’t recognize a scud if it popped up and did the backstroke in their bowl of Cheerios. Though, in waters devoid of fish, the scud population can reach densities in excess of 10,000 per cubic meter (!), they often remain undetected, due to not only their subsurface and benthic existence, but also their diminutive size (typically ranging from 5 to 20 millimeters long), adaptive coloration (i.e., camouflage), and photosensitivity, which means they generally avoid sunlight and cleave to a nocturnal lifestyle. But fish don’t have any trouble at all detecting amphipods, and in waters that are scud-dense—typically lowland lakes—trout can attain growth rates of over 2 pounds per season and reach jaw-dropping proportions. 
   Amphipoda is an order of crustaceans that live pretty much everywhere there’s water—with the exception of water with horrific amounts of pollution or acidity. Though most amphipods are marine animals—9,500 ocean-dwelling species have thus far been identified—about 1,900 species have been found in fresh water. Fortunately, for the sake of one’s sanity, only two families are important to anglers: the itty-bitty but ubiquitous Hyalella and the significantly larger but limited-range (they prefer calcium-rich waters) Gammarus. Given their almost identical appearance, the main distinguishing characteristic in determining appropriate fly pattern is hook size: 18 to 22 for Hyalella and 10 to 18 for Gammarus.
   As regards tying convincing patterns and, certainly, their subsequent presentation, it helps to have at least a rudimentary grasp of scud physiology. When at rest or dead, amphipods look like a splotchy comma—laterally compressed, with a curved back. Although in appearance a seamless unit, the scud’s body is actually divided into three regions (head, thorax, and abdomen), with seven pairs of legs projecting from the thorax. The first pair of legs—which could be described as scrunched up—function as modified mouthparts; the other legs are used for locomotion and food capture. The scud’s head bears two sets of antennae and a pair of fixed compound eyes. Breathing—via gills and an open circulatory system, including the heart—takes place in the thorax. If you want to get technical, engaging in a dissection-level study, the scud’s abdomen consists of two parts: the pleosome, from which protrude swimming legs; and the urosome, which includes the telson (tail) and terminal appendages called uropods, which do not form a distinct tail fan as they do in true shrimp. 
   Like all crustaceans, scuds are wrapped in an exoskeleton made of both calcium carbonate, as in snail and mussel shells, and chitin, the material in human fingernails. Amphipods reproduce sexually, and the pregnant female then carries the clutch of orange-colored eggs tucked away in a pouch called the marsupium—which goes a long way in explaining why scud fly patterns with orange accents or an orange bead often prove effective. The majority of amphipods are, first and foremost, detritivores or scavengers, with some species preferring to graze on algae, while others prey on micro-insects and crustaceans, including each other. To most scuds, anything dead or dying that sinks to the bottom and rots qualifies as groceries.
   Unlike the sometimes bewildering metamorphosis of aquatic insects, newly hatched scuds begin life as basically miniature adults, growing in size with each molt. What little disagreement that arises when discussing scuds primarily concerns their body shape during locomotion. In his recently released Stillwater Fly-Fishing Secrets, Hal Janssen asserts that scuds “only assume a curved attitude when they are dead or seeking protection.” Janssen ties all of his scud patterns on standard shank hooks. “Scuds swim with a straight-body attitude, rather than a curved one,” he says. “… For 98% of the Stillwater [sic] applications, the straight-body attitude yields more takes.”
   Philip Rowley at concurs: “Many anglers capturing or viewing a stationary scud for the first time may consider using a distinct curved hook to imitate their natural profile. This would be a mistake. Fly fishers need to imitate moving scuds darting through the water in an outstretched manner.”
   While it would be foolish not to defer to those far more knowledgeable, my own observations don’t entirely align with the straight-body proponents. It appears to me that scud propulsion is quite erratic: yes, for brief bursts, they are flat-out linear, but they also exhibit movement characterized by nervous, shaky lapses, replete with a drooping tail, and, at moments, skitter sideways in a more than slightly bent posture. The upshot? When tying scuds, opt to use either a standard shank or a gently curved hook (e.g., the Daiichi 1120 or Tiemco 2488H) and you’ll be in the ballpark. As always, presentation trumps pattern.
   Janssen advises anglers to fish scuds in the early morning and to “concentrate your efforts on the back side of a weed bed,” which is best probed with a “lightly weighted scud imitation tied to a 15 foot leader and a tippet section 1-½ times the depth of
the water.”
   While it may prove necessary to try varied retrieves, the standard scud retrieve—a series of short strips, followed by excruciatingly long pauses (15 seconds or longer)—often gets results. Remember, trout, especially large trout, are lazy, sneaky, and opportunistic, conditioned to casually pounce when the prey appears most vulnerable. Any anomaly in the leader should be interpreted as a take.
   Fishing scuds is a commendable way to add an arrow to any angler’s quiver. And it’s a fine way to while away a tranquil morning on the water, notwithstanding the possibility of hooking something big enough to yank the wrinkles out of one’s synapses.
   Then there’s this: filing upstairs all those obscure bio-nerd terms associated with amphipod anatomy—pleosome, urosome, telson—surely provides killer ammunition for your next Scrabble game.


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