I was involved in a recent argument about the use of the word "flea" instead of "fly" in conjunction with the sport. I conceded that I was wrong to use "flea" when describing a fly as this invertabrate is not a known prey, being unlikely to be found in the vacinity of fish. (Please don't count water fleas - that's stretching a point asd they aren't fleas at all).
Is it just another mispronounciation thing from my (second generation) ancestors north of the border

or is there a darker origin to this and if so, why don't I ever hear the term "Flea Fishing"?