Another thought, it might just be foragers returning late in the day when temps are dropping rapidly. They miss the landing board falling on the ground and get chilled. Try warming some of them in your hand and see if they then fly home.

I see this here in British Columbia mostly in March. It's a bit unsettling as I wonder how many out in the field never make it back even close to their hive. With the few hives I have I put very large landing ramps up to the entrances.    

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html