in a river’s ecosystem minimizes the potential these insects harbor for catching those hard to move trout.
Behavior
The nymph’s portly torso and stout abdomen with double equipped claws at the end of their tarsi culminate into a juggernaut like exoskeleton, prime for scrounging for food among rocks. Excluding some larger specimen such as the predatory Golden Stones, most species subsist as shredders of decaying plants and animal debris left behind on riverbeds, where they spend anywhere from a 1 to 3-year period of their life prior to emergence. During those years of foraging and survival, juvenile nymphs experience a number of instars, or molting. Dependent upon location and extreme fluctuations in water temperature as they grow and mature, this molting may take place as little or as often as 10 to 30 times throughout the nymphs’ lifecycle, equating to some species staggering 5cm (1.9-inch) size.
The majority of stonefly activity, including emergence, occurs during early morning hours, dusk and undercover of midnight skies to avoid becoming a trout’s next snack. However, if there is ever a moment worthy of note taking it is the stonefly migration called behavioral drift. During this migration nymphs freely expose themselves to currents as they shift locations on the bottom of the river. This relocation occurs daily and happens in an almost synchronized production, with large numbers of nymphs alternating holding positions in the river at the same time. This behavioral drift goes largely unnoticed by most anglers due to the time of these migrations, and by the pure and simple fact that it happens underwater; a place we all seldom visit.
Along with their migrations, there is a trait that makes them such a viable food source for trout during the day and is found in their strongest characteristic disadvantage—our greatest advantage—their inability to swim. The finely dispersed gills, single abdominal gills, or absence of gills on species such as Isoperia, attribute to the nymphs preferred location in the fast flowing sections of rivers and streams.
As they search out food or jockey for stream position, they become susceptible to the strong currents and eagerly awaiting trout. Once broken loose of their grasp, stoneflies have no other option than to ride out the drift, becoming ridged as they tumble downstream until they bump into the next obstruction. Due to the increased numbers of free drifting stoneflies during migration and their lack of swimming skills, these large succulent morsels floating past make dead drifting imitative patterns an extremely productive method when all else fails.
Every season has their nymph, and every nymph has a season of importance. With stoneflies, their importance and season are all encompassing throughout the calendar year. There is rarely a moment when I never fish these nymphs, and five select families and the species from their order always have my attention when I’m on the water, whether or not their adults are present.
Tiny Black Winter Stoneflies
Their emergence places Snowflies, Forestflies, and Needleflies at the top of the list as winter fodder for sluggish trout. Commonly lumped together under the title of Tiny Black Winter Stoneflies, these robust nymphs contain some of the smallest species found in the stonefly order, and quite often are the only actively emerging insects during those hard to fish days of mid-winter.
Target hatch times range from February to April, with continued emergence into early June in higher elevations. On Eastern Rivers of lower elevation, I have seen scores in the hundreds emerge on the brightest day in the middle of January, turning an otherwise fishless trip into one of tight lines and a wet net.
The jet-black coloration in their design allots for this winter emergence, giving the adults vital means for soaking up what little sunshine the day has to offer as they scuttle over snow banks. Spending most of their lifecycle as an adult burrowing around the snow covered ground and barren shrubs, winter stones rarely offer much in the way of substantial dry fly action. This eliminates the necessity to carry with you an assortment of dry fly patterns early on in the year, opening those slots for the more desired tiny black nymph imitations that will, if fished properly, catch trout.
No two nymph patterns are created equal, and each individual angler holds their proven patterns near and dear to their heart. Determining which ones are best suited for your home waters may take some time, but I have found that carrying a variety of nymph imitations in black and dark brown colorations, in hook size 14-18 with the occasional size 20, will cover most of the species in each of these families.
In my “go-to” winter fly box, I’m never short on simplistically tied patterns such as the classic black or dark brown Bead-head Hare’s Ear, black Pheasant Tails (with and without added flash in the wing case), and my personal favorite, Prince Nymphs. Size 18 gold ribbed, biot-body patterns, Hotwired Stones, and black/brown woven-body styled nymphs have all worked just as well for me in the past—I still carry a handful to the river and enjoy the...
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