This interesting passage comes from Evans-Wentz (177) field work in Cornwall. The motif of the four-leaved collar was common in the south-west.

In general appearance the fairies were much the same as pixies. They were small men and women, much smaller than dwarfs. The men were swarthy in complexion, and the women had a clear complexion of a peach-like bloom. None ever appeared to be more than five-and-twenty to thirty years old. I have heard my nurse say that she could see scores of them whenever she picked a four-leaf clover and put it in the wisp of straw which she carried on her head as a cushion for the bucket of milk. Her theory was that the richness of the milk was what attracted them. Pixies, like fairies, very much enjoyed milk, and people of miserly nature used to put salt around a cow to keep the pixies away; and then the pixies would lead such mean people astray the very first opportunity that came. According to some country-people, the pixies have been seen in the day-time, but usually they are only seen at night.’