Time came to thwart their efforts so I circumscribed a line of chalk around the vent and that stopped them. Hope the ones who couldn't return found another route. I bet so as their sisters have found other routes in though we marked them off too. Haven't seen any in a few days. There were more persistent ants on the balcony of our hotel room in Bangkok and I drew a circle around where I sat there and noticed that some got through - they were bigger. Not that big a deal cause they weren't biting ants which seem to be only the bigger red ones. Here's Wikpedia on this most noble stuff.
