For some reason I've found they seem to be attracted to rye beers. I've had two rye pale ales that (back when I fermented in a large bucket) attracted them, one of them lost to infection. More recently (and brewing/fermenting in a different town entirely) I've had them show up in my fermentation fridge while fermenting a rye saison. I now have a fermenter that is sealed except for the blowoff tube, so they had no way of getting to the beer...