We've gotten substrate from two different suppliers and I've even froZen it for 5 days prior to use to make sure it was pest free. I think maybe because I've had so much rain in my area. (Virginia) that they are coming in from outside and just so Happen to find wood to eat in the enclosure.. my issue with them is they were getting bad. I could see them climbing on the outside of the tank as well as inside along the bottom and also on the wire rack that holds the two 30 gal tanks . My son tanks his snake out almost daily and when I can see wood mites crawling on him I don't even want him to touch him and get them spread around the house. I may have to find a more mild bug spray to just use in the room and do the baseboards and windows so they don't even get in at all.... It's just so much work to take down 3 whole tanks clean and reset up again. The last two times were 4-5 hours ! .