Larger dermestids are quite easy to keep as a reproducing colony. I thought my small one had pupated inside its larval skin, but maybe it simply died. I recently dug through the material in the small plastic container in which I was trying to rear it, found it, and dropped it back into the container. It sounded like a hard seed hitting the bottom. I suspect it is dead and dessicated.

That said, I fed it and watched it grow, giving it high-protien foods like a piece of puppy chow and a couple pellets of dried shrimp fishfood, and just a little water from time to time. They don't need much. After all, this one was found living in the glass shade of a ceiling light, eating the dead bugs there. You might feed yours some dead bugs...

Good luck.