Prior to the writings of G.E.M Skues emphasizing the importance of the nymph, most of the old English wetflies and Yorkshire spiders were dressed to simulate the adult phase of waterborn naturals, a phase that, at times, can be more important than the nymph, particularly with larger insects like green drake, October caddis, or the larger stonefly species producing seasonal emergences and a lot of adults accumulating through the hatch season.
In the West, skwala stoneflies signal the beginning of the year’s parade of water-born insects and are a real opportunity for hatch-matching while there is still snow on the ground.
The need to “match the hatch” was a facet of trout fishing with flies that intrigued me the most as a young angler and still abides as a source of entertaining and satisfying challenges. It’s an aspect of our game that separates steelhead and salmon fishing from trouting. Trout are actively feeding (more or less), a habit that adds quite a bit of nuance to our angle of pursuit, including presentations outside the classic step and swing salmon/steelhead approach.
Admittedly, the effectiveness of a fly relies principally on the confidence that the fisherman has in it, but it also has to be recognized that the nearly-doubled rate of success kills any prior prejudice; the PHP flat-out works.