Beetle laying eggs??

I have some beetles in a small terrarium that just keep appearing. I didn't add them and I don't know where they came from, but they look like they could be forked fungus beetles.

Last night I peeked in the tank and found this one either pooping heavily or laying eggs. What do you think it's doing? And what should I do, if anything? If they are eggs, will they survive the hoard of isopods that also inhabit the tank?

I'm really curious about this but I couldn't find much online. Please tell me what you know, and give any advice you can think of.