Whether you are faced with an hatch of olives or the fish are latched onto terrestrials, spiders work a treat. Fished upstream, they work well fished just under the surface. A deeper presentation can be achieved if they are fished with a heavier nymph. Here's an example that works well, espeially when faced with those frustrating, dimpling rises.
Hook: Partridge SLD #16
Thread: Sheer 14/0, orange
Hackle: Greenwells Hen
Tag: Tying thread
Rib: Hends 0.09, gold
I find tying a thorax, but leaving a longer section of bare hook can be very effective. Perhaps the hook helps the fly's translucency?
When fishing the upstream spider for grayling, watch for the flash of sliver as the fish turns to take the fly - this gives you an early sign of a take well before the leader moves.