They are pervasive little buggers. I used to build boats for a living and we had a bunch of wood filler dust (epoxy additive) come in with wood mites they got everywhere. We ended up spraying insecticide everywhere. Sadly with snakes that isn't an option. I hope you can get rid of them. I never buy wood products (mulch ect.) from garden places. I have seen far too many wood mites and aphids in and on it. I personally use compressed coco coir that so far is free of extra stuff but the odd stone and seed.