Smaller T's like to burrow. If you checked the substarte REALLY good and all the possible places it could be in the enclosure then I don't know what could have happened if it was escape proof Did anyone happen to open the container that you are not aware of? Maybe they left the lid off and it escaped and they put it back on later? Maybe it bolted when someone else was looking at it and they didn't see it? I don't know Just throwing out thoughts your way. Hope you find it though!!!