WD-40

Tying the WD-40 is straightforward, though working at tiny hook sizes requires good lighting and magnification. Begin with a size 18-20 hook until you're comfortable, then progress to smaller sizes. Start by securing a small clump of Z-Lon or antron fibers at the bend to create a trailing shuck extending about half a shank length. This shuck represents the nymphal skin the emerger is shedding, a critical visual cue for selective trout. Keep the shuck sparse—a few fibers are sufficient.

Build the body using only the working thread, wrapping forward in tight, touching turns to create a slim, segmented appearance. The original pattern called for exactly 40 wraps, but simply wrap to leave about one-quarter of the shank behind the eye. The thread body should be smooth and slightly tapered, thicker at the thorax. Color matters—olive thread for Baetis and olive midges, brown for larger mayflies, and black or gray for winter midges. Some tiers coat the body with head cement or UV resin for durability and a slight translucent sheen.

The thorax consists of a small amount of superfine dubbing in a color matching the natural insect. Keep it sparse—just a wisp of dubbing creates the proper profile. Before or after the thorax, add a single CDC feather tip as an emerging wing, tied flat along the body or slightly upright. The CDC should extend to about the hook point, suggesting the developing wing of the emerger. Some variations use poly yarn instead of CDC for increased visibility, while others omit the wing entirely for an even simpler pattern.

Fishing the WD-40 effectively requires understanding emerger behavior and presentation techniques. The fly works best in the surface film or just below, positioned at the exact depth where natural emergers are trapped. Use a long, fine tippet (10-12 feet of 6X or 7X) to achieve drag-free drifts. Fish the pattern as a single dry fly when trout are rising visibly to emergers, or suspend it beneath a small parachute Adams or similar dry fly for increased visibility. In slower water, watch for subtle rises—often just a nose breaking the surface or a slight dimple. Set the hook gently with a smooth lift to avoid breaking the fine tippet. During heavy midge emergences, focus on feeding lanes and seams where trout hold, sipping emergers with rhythmic rises. The key is patience—match the hatch precisely, achieve perfect drifts, and be ready for technical fishing that rewards skill with consistent success on selective trout.

John Barr developed the WD-40 in the early 1990s while guiding on Colorado's South Platte River, one of America's most technical tailwater fisheries. Barr recognized that during midge and Baetis emergences, trout often ignored nymphs and adult imitations, focusing instead on the emerger stage when insects were trapped in the surface film. Existing emerger patterns were often too bulky or complex, failing to match the slim profile of natural emergers. Barr's solution was elegant simplicity: a thread body with minimal materials creating a realistic emerger profile.

The pattern's name reflects both its simplicity and its effectiveness at solving a difficult problem—much like the famous penetrating oil it's named after. The WD-40 quickly gained popularity among Colorado guides and technical anglers, who found it consistently outfished traditional patterns on selective tailwater trout. Barr's pattern arrived at a time when fly fishing was becoming increasingly technical, with anglers studying entomology more carefully and demanding patterns that precisely matched specific insect life stages.

The WD-40 spread beyond Colorado as its reputation grew through guide networks and fly-fishing media. Anglers fishing technical waters nationwide—from Pennsylvania's spring creeks to Montana's tailwaters—adopted the pattern and often modified it slightly for local conditions. Variations emerged using different thread colors, dubbing materials, and wing options, but the core concept remained unchanged: a slim thread body with a trailing shuck and minimal thorax, creating a deadly emerger imitation.

Today, the WD-40 is considered an essential pattern for any angler fishing tailwaters or spring creeks where midges and small mayflies are important. It represents a broader trend in modern fly tying toward simple, effective patterns that imitate specific life stages with precision rather than relying on general attraction. John Barr's creation demonstrates that innovation doesn't require elaborate materials or complex techniques—sometimes the best solutions are the simplest ones, executed with attention to the details that matter most to selective trout. The WD-40 remains as effective today as when Barr first tied it, proving that fundamental principles of emerger design transcend changing trends and temporary fads in the fly-fishing world.