The Light Cahill Parachute is a mayfly imitation. Fish it dead drift.
The term "parachute" comes from the manner in which the hackle is wound: horizontally, above the hook, truly creating a sort of parachute appearance and effect. The parachute-style fly was designed to give better visibility to the angler in bad-light situations with small dry flies. The benefits of the parachute style are that the position of the hackle really helps the fly alight upright and that the hackle fibers radiate around the thorax as do the legs of most trout-stream insects.