The monarchs have finally eaten themselves out of house and home. All that remains of the milkweed plants are the stems. There are still caterpillars on them. Most are big enough to move off and pupate. And in fact, if you walk away from the denuded milkweed in any direction, you will find many pupas, as well as caterpillars looking for just the right spot to make that final moult.
Some of the caterpillars that remain on the milkweed are trying to eat the stems. There are a few small ones that will probably not survive. The yellow aphids, who don’t need leaves, crowd along the tops of the stems, sucking the last bit of nutrition from the barren stalks.
A few of the pupae are defective, doomed never to complete their metamorphosis.
This one is questionable.