I don’t know if W.C. Stewart had yellow sallies or sulphurs on his wee Scottish burns. But we have them here in the States, and Stewart’s Dun Spider does a bang-up job of imitating those hatches. Try fishing this on a small stream as a dropper off a bushy dry — or as a dry-wet tandem during a sulphur emergence. (You can thank me next time you see me.)
Every fly tier has a good supply of dotterel on hand…uh…hold on…dang! Turns out, not so much, even in Stewart’s time (mid-19th century). You can substitute with webby dun hen, or heed the sage advice of the man himself:
Stewart’s Dun Spider