Here's a marvelous explanation of the Irish "seven devils" as speculative superstition refracted by a mental prism into differently colored devils across the nations of the earth.  From Holland-Tide or Irish Popular Tales by Gerald Griffin, 1927.  Favorite phrases: "If one were disposed to be fancifully metaphysical upon the subject ..." -- yes, one would be so disposed!  Ireland as a "step-daughter" island.  And the zinger: "But what has this to do with the story?  In order to answer that question, the story must be told."