Mites are species specific so they wouldn't have come from the feeders. As for the mites being wood mites, I don't know about that. I know it is possible to get mites from cypress mulch, so I assume Aspen would be the same.

Are you positive you have mites? I was using Aspen at one point and I was pretty sure I had mites, and I treated my tubs for it, but looking back I think it might have just been super dusty Aspen. If you have been around any other snakes then you might have picked up mites from them and brought them back with you.

If you are positive you have mites, order a can of provent-a-mite and follow the instructions. If they came from the Aspen and you want to prevent that in the future you can switch to news paper or paper towels. It doesn't look as nice, but it's easy to clean and you don't have to worry about mites.