Brownies are somewhat unusual among the wider groupings of fairies because they prefer to live with or near humans, either in human homes or in mills, although some have also been connected to bodies of water like ponds. Brownies in mills come out at night and work in the mill, not always in a way that helps the human owners, while Brownies in homes come out while the human inhabitants are sleeping and clean. Overall Brownies have a good reputation as helpful spirits, however, in older folklore they were seen as ambiguous beings and potentially dangerous particularly to those outside their chosen family, although even that family could be on the receiving end of the Brownie’s destructive temper if it was angered.
In descriptions Brownies are usually, as the name implies, a nut-brown color and are said to dress in rags. This style of dress may be a preference as stories tell of the unfortunate results of well-meaning humans offering their resident Brownie a new set of clothes. In best case scenarios the Brownie snatches up the clothing and leaves forever, sometimes singing happily that the new clothes mean that they will not work anymore; worst case scenarios the helpful Brownie is so offended it transforms into a malicious Boggart. This may be because the Brownie is bound to service and can only be released with purposeful payment, or because they are mortally offended by any implication that they are serving humans.
When Brownies appear in folklore the focus is usually on their role around human homes or farms, and secondarily their place at mills. Around a home they are known to do chores while on a farm they will help bring in crops and tend to the livestock. In one story centered on a mill, a human girl goes to grind wheat after dusk only to find the mill occupied by a Brownie who she douses with boiling water when he gets too amorous with her; he flees to his mother but later dies of his burns.
Brownies must be paid surreptitiously for their work, with food being left out for them but never directly given to them. A household with a Brownie would be expected to leave a bowl of milk and small loaf of bread or cake out once a week to show their gratitude for the Brownie’s efforts. This food and drink should be left without verbal thanks and not directly as a gift, but placed carefully where the faerie would find it to avoid any chance of offending them. In this we see a juxtaposition of careful preparation and seemingly casual placement, with the housewife ensuring the Brownie’s continued effort for the household this way
Besides leaving if given clothes there are a few other things that will force a Brownie to leave a location. Several accounts of Brownies attached to homes describe the faeries being driven off by well-intentioned efforts to baptize them or reading from the Christian Bible in their presence, two things these faeries apparently cannot tolerate. Farm-oriented Brownies will become destructive and leave if the quality of their work is insulted or more generally if a person speaks ill of them.
Mark Bere Peterson’s Counterculture, Urban Legends, Paganism & Witchcraft 