Filthy Little Devils
ASK 10 FLY FISHERS WHAT THEIR favorite leech pattern is and a healthy proportion will answer, “The Woolly Bugger.” This iconic fly is a proven fish catcher in water both flowing and still. However, trout anglers who spend a lot of time on productive stillwaters are learning that small, imitative patterns fool trout more consistently.
Once thought of as an incidental snack, it turns out leeches can make up a large part of a trout’s diet. While anglers rarely see leeches free-swimming in the water, it does not mean the fish are not looking for them. Studies show that leech densities can reach more than 500 individuals in a square yard of substrate! Their importance to trout is further verified by how often a hooked fish regurgitates leeches during a fight or when landed. What is even more revealing is how often anglers find small or juvenile leeches, which we call micro-leeches, in the throats or stomachs of fish. This is especially pronounced during spring and fall, the best times to take trout on leeches.
Sheridan Lake is a very large, extremely nutrient-rich, blue-ribbon trout fishery in British Columbia’s Cariboo region. The lake is famous for growing big rainbows; they often reach the mid-teens in weight. The lake’s most prominent feature is its vast, marl-bottomed shoals that vary from three to 15 feet deep. In the late fall, dropping water temperatures bring big trout onto the marl flats to feed primarily on small scuds, which are very abundant. You can often see these huge fish swimming slowly along the bottom, their bellies in the marl as they tip their heads down to eat another scud. It is extremely difficult to fish scud patterns with any amount of success when there are so many real ones around. But these fish will regularly take a micro-leech wind-drifted under an indicator and suspended barely off the bottom. The bite is very subtle, so paying close attention to the indicator is critical to hooking up. Some of my most memorable days have taken place on Sheridan Lake while watching those fish eat a micro-leech and then take off down the flat as if they were bonefish. This is a tactic that may work on your homewaters, too, so it makes sense to pack these micro-leeches to all of your trout lakes.
Leeches are members of the Annelid (segmented worms) family and can live for 15 years. More than 60 species have been identified in North American fresh waters. They range in size from less than half an inch to over five inches. Some species when fully mature measure an astonishing 16 inches long. All leeches are most active at night—during daylight hours they often seek cover under logs, rocks or benthic debris. They sometimes bury themselves within the silt or mud bottom interface. Trout have to actively search them out, which confirms the leech’s status as a preferred food source. The majority of leech species are scavengers, feeding on both plant and animal matter. Their feeding strategies and sensitivity to light are prominent reasons why leeches are found close to the bottom and often in or under some form of cover.
Leeches exist in a wide range of colors, with black, brown, reddish brown, maroon and green being quite common. Many leeches are multi-colored, with black and brown and shades of green and brown. Prime leech habitat is the bottom or benthic areas of a lake’s shoal or littoral zone, in water up to about 25 feet deep. Their bodies are dorsoventrally flattened (from the back to the belly) and they have anterior and posterior suckers. These suckers are used to move along substrate in a looping or inchworm motion. Leeches are also excellent swimmers, moving through the water in an up-and-down action like a sine wave. When they are disturbed or attacked while swimming they curl into a ball and fall down through the water back to the bottom.
Leeches have a very slender profile in the water, which should be considered at the tying bench. By far the majority of species are small, so when fully extended and swimming they range between one and three inches. Smaller or juvenile leeches are a highly preferred food item, perhaps because they are easier to catch and are often found in higher densities than the adults. Regardless of the reason, stillwater trout have a fondness for micro-leeches. Small means patterns tied on #10 2X long to #14 2X long nymph hooks, on scud hooks in #10 and #12, or balanced on a jig hook. Soft, flowing materials, including strung and Woolly Bugger marabou, rabbit and synthetic dubbing, are ideal for creating patterns that undulate or pulse when retrieved or wind-drifted.
One of the most effective ways to fish leeches is under a strike indicator, whether wind-drifted or retrieved with the occasional short pull. The perfect indicator presentation, in my mind, is to cast directly into a gentle breeze and then allow the indicator and leech to drift back to you. Just keep stripping in the slack so that the line remains tight. The natural up-and-down motion of the leech, in combination with a slow, horizontal movement through the water, is almost irresistible to passing trout. The key to this technique is to have the leech suspended within about a foot of the bottom and moving slowly through the water. When lake fishing, I always use a non-slip loop knot to tie my fly to the tippet (except when I’m fishing dries). The loop knot allows the leech to swing and undulate naturally when suspended under a strike indicator.
Another effective method is to cast the indicator and a beadhead micro-leech into the openings within stands of longstem bulrush, cattail or pondweed. Let wave action move the indicator up and down and wait for the bite. You would be amazed at how many trout are cruising around and through those dense mats of vegetation looking for bugs or other invertebrates.
Leeches can also be fished with a floating line and long leader. I like to fish this method along the edges of drop-offs, where there are always fish cruising in search of food. My preferred setup is to anchor on the inside or shallow edge of the drop-off and cast out over the edge. Once the fly sinks close to bottom I start a very slow, four- to six-inch strip retrieve, allowing at least 10 seconds between pulls. Alternatively, if there is a slight breeze blowing down or parallel to the drop-off I’ll wind-drift a micro-leech along the sloping face of the drop-off. In either scenario my leader is at least 25 percent longer than the depth of water. This extra length ensures the fly will stay close to bottom during the retrieve or drift.
An alternative to casting long leaders is to fish with full-sinking lines, ranging from intermediate to type 3 sink rates. Let the fly line get the leech down to the desired depth. Slow but continuous hand-twist retrieves interspersed with an occasional couple of quick pulls is a good method to try on shoals and over the drop-off zones.
This spring, and again next fall, try downsizing your leech patterns in conjunction with the tactics described. I think you will be pleasantly surprised at how effective small leeches can be. w
Red Ruby-Eyed Leech
Hook: Mustad R74-9672 Streamer 2X heavy/4X long in #10, #12
Thread: 8/0 black
Tail: 50/50 mix of black/red Arizona Simi Seal and red Arizona Simi Seal
Body: Dubbing brush, using small red copper wire and same 50/50 mix of Arizona Simi seal
Cone: 1/8’ gold conehead followed by medium silver-lined red bead
Peacock Micro Leech
Hook: Mustad R72, Long Nymph 2X heavy/2X long in #12, #14
Thread: 8/0 black
Tail: Black marabou fibers with 2 strands of red Krystal Flash
Rib: Fine red copper wire
Body: Arizona Synthetic Peacock dubbing
Bead: XS red glass bead