I believe (don't quote me on this) most of the speceis we can get in the U.S. do well at 72-78 F. I do not mean to worry you. Some millipedes start to have a die off above 80-82 F. Let me see what info I can find out about your species. Maybe no big deal with bumblebees.MrCrackerPants, I'm having a hard time finding anything talking about temps.
In Millipedes in Captivity it only says they need to be over 72*
Bugs in Cyberspace says room temps.
My problem is I need to keep the T room up because I have some younger snakes in there. If I take them out of that room the room temps fall into the 60s at night.
Do most millipedes fall into the 75-80 range?