I have gotten various pests in different bins. I have seen small beetles as well. They probablly aren't harmful, but I'd just throw them or sift them out. They could be weevils attracted to the oats or grain you use as a substrate. Mealmoths are a really bad invader and can throw a whole mealworm or superworm colony into chaos. The beetles aren't as problematic or difficult to get rid of. Some people sometimes have their colonies with open tops, but it is wise to use a screened lid of some type.