Well, I recently swapped some outworlds around. I connected a well-vented outworld to my P. rugosus colony so the seeds I supply are less likely to get moldy (like the first batch did). The outworld has two offset holes, I rearranged everything a couple times and finally settled on the best-fit for all the colonies on my ant shelf in the garage. Today I noticed a wandering rugosus worker on the floor, scooped her up and figured I left the lid loose when feeding yesterday. To my surprise, when I peeked under the red darkscreen, except for the second worker the nest was empty! A closer inspection revealed that a week ago when I swapped the outworlds I never plugged the second hole, so I've been feeding an empty nest for at least a few days - having not peeked under the darkscreen since the outworld swap. The queen left and took her brood with her, leaving her two workers to fend for themselves.
A first for me, a royal escape, I wish her well! I'm hoping she turns up around the garage somewhere. Plug those holes!