This is not to be confused with the dry fly Spider. This represents a terrestrial spider, blown onto the surface. It definitely has a niche in the fly box.
Hook: Mustad 94840 size 8 - 14
Body: closed cell foam
Legs: coarse hair
Thread: Monocord
This is a pretty simple fly. Lay a foundation, tie in the rear section of the foam, tie in four hairs, tie in front section, finish with a wrap knot and cement. Bend hairs with a straight edge to resemble spider legs and coat hairs with dry fly prep (whichever form suits the angler best). The secret to tying this one is preparing the body. The rear section is split, tied in from below, and the fore section is not split, forcing the hairs upward as the foam presses against the shaft.
I personally use my own hair for the legs, for it is blondish, very straight, very coarse in terms of human hair. (Women used to envy me my hair.) But a number of pale hairs are coarse enough for the task. Horse mane and tail is very suitable. Make the bends noticeable, but not too sharp, or there will be problems with twisting when the casting begins. If you've ever seen a spider on the surface of the water, the legs are usually spread out. This is the position to mimic when the body foam is floating on the surface. Try to mimic the imprint on the water from below.
Dead calm is the key here, letting any wind provide the sole motion. This fly is not suited for skittering. Cast and let lie on still water. Cast and mend diligently on moving water. That's about all there is to it. But don't discount the effect of this little sitting duck has on the fish. Constructed properly, this is a ringing dinner bell. Cast and let the fish do the rest.