Thank you everyone. I am definitely going to be freezing stuff for longer!
Just to clarify: These bugs are minute. Like specs of dust. As I say, it was only because Mimi got a fair few of them proliferate when she was a sickly old lady that I have been looking out for them now - I couldn't possibly see them on Percy or on his bedding; I can only spot them by staring really hard at his smooth wooden lid and waiting to see if any dust specs move. Like, they are tiny. So I am still in two minds that really they might be normal hamster mites. Hubby took a photo with his macro zoom lens and we could just about see the spec had legs when he zoomed it in 100x! So when I say I can see them I'm not talking flea size or anything...
In any case, I have squished the 3 I found yesterday (spotted by shining the torch on the wood and waiting for anything to move!!) and there was no sign of any on Percy's house wall. He seems less itchy so perhaps the substrate change worked; he even tolerated my brushing him with a toothbrush last night so perhaps any remaining mites were removed! (He allowed me to bathtub train again last night; the night after I had changed all his bedding and substrate in that end because I'd spotted mites, he was NOT amused and sat in his bedroom in a grump - poor Percy!)
Anyway, minor victory: he's starting to use his potty in his other chamber of his house! So at least that's something good to celebrate!
