A "red quill" is an artificial fly used in fly fishing on rivers and streams to catch trout. It represents one of many types of May flies that hatch in these waters. The technical name of the fly is Ephemerella subvaria and is the male representation of the May fly. This is the only May fly that has different coloration by gender.
This fly was originally tied by Art Flick in 1933 and he borrowed the name from an old English fly that was made many years before. His original "recipe" (fly tying books will refer to the materials used in making a fly as the recipe) are:
Wings: flank feather of mandarin or wood-duck drake Body: quill of large hackle feather from Rhode Island Red cock, stripped and well soaked Hackle: natural blue dun Tail: few wisps of dun spade or barb feather Hook: No. 12
In "Art Flick's New Streamside Guide to Naturals and Their Imitations," he explains the optimal time to be considering the use of this particular fly.
"This fly like all others is affected by high water temperatures. On streams that tend to heat up, it will often emerge in the evening instead of its normal emergence time in the afternoon. Under normal conditions it will appear at almost exactly the same time every afternoon, to such an extent that I have heard many fisherman remark that you could almost set your watch by it."
Writer's comment: Although I have used this fly to catch fish, I don't use it often. Given the commentary from the book quoted above, I guess I shouldn't expect to use it a lot. But I did think it would be catchy name for a consulting firm.
Still curious? I have a display of three types of red quill flies, four sizes each, that were tied by professional fly tier A.K. Best in my office. You're just going to have to visit!