I have found several of these unusual green caterpillars buried deep in the tender new growth on the tips of stems. I think they cause the rot at the base of the stem where the leaf begins. The new growth is what the tiny brand new Monarch larvae also prefer. I didn't notice these green caterpillars until mid October. I have seen white butterflies laying eggs lately, but not on milkweed. I didn't find this caterpillar on the ID searches I did. Anyone know what these are? I enlarged the pictures, they are fairly young ones, barely detectable, but I was using a magnifying glass looking for tiny Monarch larvae, and that's how I found them.

They have a strange head, sort of pointed. They have an odd way of moving, it's fast, and with amazing agility they bend and curve around tiny leaves and larger stems. They seem to raise up in the center a little when they move forward, and it raises it's head up and whips it around fast. It seems to have a stubby beige "nose" .

It doesn't have fur, those fibers are some traces of a mohair sweater I was wearing that was shedding.

Since the Monarchs are still laying eggs (it was around 80 degrees today) I cut back the milkweed 50% in Sept. and have fertilized it, and it has quite a bit of nice new growth. But the nights are getting cold, so I'm raising the eggs indoors. I'm pushing the milkweed growth to insure having enough food for the Monarch eggs that I have and others to come. Last December I had hungry cats and ran out of milkweed.

So I wasn't happy to see these caterpillars eating away at the tender new growth--anyone know what they are?

I don't think that I am able to upload several pictures at a time, so I'll post this one.