Do you by chance have any birds in your barn, nesting pigeons or barn swallows, or perhaps chickens? I just had this very same problem in my barn last week (we are in Colorado though) and it turns out they were a type of Mite- YUCK is all I can say.
They are nocturnal and they come from birds or poultry. They typically attach themselves to the surrounding environment then come looking for something to feed on at night. To get rid of them you need to spray your barn down with permethrin or use Poultry Dust. I did both just to be safe. Then (after looking all over) I found a little nest of barn swallows up in a rafter and the little beggers were all over crawling out of there-ewwww. If you google chicken mites there are several really good articles on what they look like and how to get rid of them! I went to the garden store and got a large container of Sevins Dust which is a garden product for lice, mites, all types of bugs it was a little cheaper than the Poultry dust to do the whole perimeter of the barn with (along the floors and walls-it suffocates the bugs), then I got small cans of poultry dust and Horse de-licer and dusted all our horses just as a precaution since for some strange reason poultry and horses are the onle 2 species which can cross contaminate lice/mites. Poultry mites can also bite humans which is gross and irritating but they can not survive long term without a more suitable host-at least that is what I read.
Good luck-I hope you find out what they are and how to get rid of them!! I seemed to have been successful with mine by doing the spray down and dusting then repeat 3 days later. I have not seen any since!