I had great luck with this one out on Monomoy and Brewster Flats... the "easygreen" crab fly:
Hook: TMC 811s, circle hook, or other SW quality hook.
Eyes: non-toxic barbell eyes. Note the other fly is tied with weight inside the felt body, no eyes - as an optional method.
Frame: 50# monofilament loop tied crosswise to shank with cut ends on same side (they become eyes). Make loop like a figure 8 with the top cut off at the eyes, tie the "waist" of the loop to the shank of the hook. Substitute extruded lead for monofilament frame if omitting eyes to keep crab rightside up.
Tail: single or double mottled marabou flank feather tied in to center and laid on top of rear loop.
Legs: green rubber with speckles, or your choice. Lay like a madam X fly and cross wrap to hold in place
Body: tan craft felt topped with green craft felt (craft store) cut to match and glued like a sandwich over the mono loop, legs, eyes and tail feather. I prefer a gel-style glue that does not harden the felt... this rules out superglue, zap-a-gap, etc. I had good luck with plumbers goop believe it or not. Aquaseal is good but pricey and hard to work with. I've not found the perfect glue but you want one that preserves the fuzziness and ligth weight of the felt while offering durability.
Markings: pantone permanent dye pen... make various markings like a crab
Eyes: melt the tips of the mono, make sure they are not allowed to touch each other
It's simply a mind-blower to crawl these flies on the sand, twitching them slightly and watching a cow turn and inhale a pound of sand with the fly.
!!! Stripers crush crabs with their rear mashing plates (in the throat) so crab flies are easily swallowed. Set the hook right away or use circle hooks. I have begun to tie them on circle hooks (the one standing up to show underside is a circle hook).
More experimentation to follow.
Juro