I find that when you tame an Aphid or Weevil they tend to regress back to wild if not placed in a pet house. That being said, however I DID place my pet Weevil into a pet house, and my friend I'm playing with placed his Aphid into one- his Aphid is now back to being scared of us but sticking around base. My Weevil....just started walking away, and didn't stop. We couldn't interact with either pet aside from just dropping slurries on the ground. (didn't drop enough to re-tame) We did find out if an ex pet is killed they'll drop whatever pet hat they have on. R.i.p Green Bean and Weevil Knievel, gone but not forgotten.