I brought in a monarch caterpillar to watch last weekend. I have him in a little terrarium on my windowsill with some milkweed for munching on. He seems satisfied with the arrangement, as far as I can tell.
At first it didn't really seem like he was growing all that much, but these past few days he's really started getting nice and long and fat. I can't believe how much he eats! I've been giving him five or six milkweed leaves every evening--leaves about twice as long and wide as he is--and they're usually decimated by the next day. And, although I shouldn't be surprised considering what I just said, I also can't believe how much he poops! It's not really messy--I have a paper towel at the bottom of the terrarium that's easily changed each day--or smelly, but given his size the quantity is a little unnerving.
Although I admit I'm easily entertained, he's just a lot of fun to watch.