There are several interesting points made on the above website.
The statements that stood out to me are the ones that very much are the same as for tenkara fishing and traditional tenkara kebari & how they developed on similar high gradient streams:
" … The streams in the north of England have stony bottoms and fall comparatively steeply out of the hills and into lowland areas.
… The interesting thing about the North Country spiders is that they seem to have little in common with the Scottish “spider” patterns beyond the name and indeed they represent a quite separate line of development.
North country spiders are very sparsely dressed, with as little as a single turn of soft hackle and they are designed to be fished upstream, with as much of the line held out of the water as possible, hence the long rod. …
It is far more difficult to imitate a perfect insect and to afterwards impart to it a semblance of life in or on the water, than it is to produce something which is sufficiently near a resemblance of an imperfectly developed insect, struggling to attain the surface of the stream.
Trout undoubtedly take a hackled fly for the insect just rising from the pupa in a half-drowned state; and the opening and closing of the fibres of the feathers give it an appearance of vitality, which even the most dextrous fly-fisher will fail to impart to the winged imitation. … "
The rest is also interesting reading. Maybe you will enjoy reading it.