Around Wisconsin, they don't make themselves very well-known at all until Indian Summer kicks in late September to middle October, and that's when they start to swarm. The article indicates that this is when they start to invade houses for hibernation, but the swarms also occur outside as well during this time, and you would think they'd be heading indoors when it gets colder, not hotter.  It looks more to me like they actually start to dramatically increase in population at this time as well, not just looking for safe warm places to hide. Have there been any studies on what is actually happening? 69.95.234.21