I believe you nailed it.

I didn't understand the sequence... I thought that what I was looking at were the "eggs" and the "caterpillars" were the results. Instead, the "caterpillars" had grown from tiny eggs, and were turning into the brown pupae, after which they would have metamorphosed and flown away.

And yes, there was a food source -- for the past few days there had been a plastic bag full of kitchen trash, carefully tied off (but obviously not tied well enough!) stuffed into the box.

At least now I know that if I missed a few of the pupae (inevitable, I think) the worst that will happen is that in a few days they will fly away.

The depth of knowledge and ability to research that is evident on this bbs never fails to amaze me.

tanstaafl.