Cut one of the smaller Chartreuse Mop fingers from the edge of a car-wash mop head, then pull the fluff off the cut end until you get down to the four core strands.
Set a standard nymph hook in the vise and start the Chartreuse Thread, wrapping back to about halfway along the shank. Leave the fly unweighted for neutral buoyancy, or add a bead or lead wraps if you want it to sink.
Tie the mop finger in where the thread ends so it runs about one shank length, binding down the fatter fluffy part and tidying it up.
Even up the Black / Chartreuse Rubber Legs, tie them in right at the back of that tie-in point and spread them one to each side, leaving them sticking off the front about one and a half shank lengths.
Bring the thread forward about halfway to the eye, take a couple of wraps in front of the legs to hold them out to the sides, then run the thread up to just short of the eye and back.
Make a dubbing loop two and a half to three inches long and wax it well with beeswax. Pick long fibres of Black Rabbit off the hide and lay them into the loop straight, a big clump at a time, rather than rolling them into a noodle.
Spin the loop up, then brush the fibres out with a dubbing brush so they stick out to the sides in a nice fat brush.
Pull the rubber legs out of the way and palmer the brush forward, stroking the fibres rearward as you go and pulling the front legs back as you reach them. Take an extra wrap in front, tie the loop off and cut it.
Pull all the hair back, wet your fingers to control the static, build a small chartreuse thread head as another hint of colour, and whip finish.
Trim the front legs so they show past the puffed-out hair, then straighten the rear legs and cut them a little past the hair. Brush the fly out and pull off the loose hairs.
Substitutions
Body instead of Mop chenille (microfiber): Cream mop chenille — Standard caddis larva color; Chartreuse mop chenille — Bright attractor, very visible; Tan mop chenille — More natural; Pink mop chenille — Worm/egg crossover color; Olive mop chenille — Caddis/crane fly larva color; White mop chenille — Clean, visible in dark water
Bead instead of Tungsten: Fl. chartreuse tungsten — Adds hotspot; Black nickel tungsten — Subtler look; No bead. Just lead wraps — Slimmer profile
Other versions
3 more in the app: Classic Recipe, Fischer's Flies, Tungsten Jig Mop.