I am about to finish reading "Two Centuries of Soft Hackled Flies" by Sylvester Nemes.
He explains that spiders is an old English term for soft hackled flies. Some of the most famous are the Black or Red Spider and the Partridge series, Green, Orange and Yellow.

These spiders are very effective because the soft hackle moves back and forth in the water creating movement and a life-like appearance.

I have not tied any of these flies but after reading the book, I certainly plan some tying this winter.

Great Book by the Way.

If you can't Fish read about it.