Zophobas morio

We got some crickets in the post today, so I put them into a tank we use for feed insects, and there were some Zophobas morio worms in there still. Z. morio is a long wriggly worm when it's a larva, and this is the form in which it's used as spider food. I was surprised, because we haven't had new Z. morio in for months, and I'd assumed that if there were any leftovers they'd be dead by now. But then I noticed the large number of small brown-black beetles in the tank and realised that the worms were (at least) second generation. I don't think I'd ever realised what they looked like when they grew up before: they're small, about a centimetre across, around the size of a new halfpenny.