If your container is losing humidity, that means there is TOO MUCH air flows going on. You don't need many large holes to have your beetles breath. Try to keep it minimum. I rear my scarab larvae in about 16 - 32 oz bottles with two to four holes (1mm diameter).
1mm is about 3/64 inches.. Think about the size. It is VERY SMALL, but still good enough size for the beetles. Beetles do not breath continuously like humans, so they do not need to have a big holes on their containers to keep up with fresh air going inside. The air flows well even without such a big holes, and the capacity needed for beetles breathing shouldn't be huge anyway. (it is such a small creature). In case of larvae, I use 16-32 oz food containers available from Dollar Tree. Anything is fine, you just have to punch couple holes. In case of adult beetles for reproduction, I use Sterilite containers available in Walmart, and many other larger containers. In case of those (USUALLY) do not need to make extra holes as air can freely flows in. Try place some water in the container, and have it upside-down, and see if water leaks freely. If it does, no extra holes need.
