I had a hermit doing the same thing. One day the 1.5 inch turbo snail shell from a unsuccessful addition was up on a rock... One of th elittle hermits had moved into it... I swear that you coudl have fit 2 or 3 in there , I don;t get how he moves it lol
But ya get some more shells from a LFS Hermits will thakn you and they may not have to steal a shell from a live snail