Those are "cleaner crews". They eat the dead crickets and the shells/sheds. They are a darkling beetle. Just leave them be, or better yet gather them all up and make a culture and then put them back in the bin. The time i got "lucky" and got 8 or so of them, but then the supers had their way with them, and no more free cleaner crews. They are worth up to a buck each on some sites that will sell you a dozen or so.