That's a hornworm that's been parasitized with wasps. Clip the leaf and set in a part of your garden away from your plants. Those pupae will spawn more tiny wasps to search and destroy more hornworms.

Search the rest of your plants for more. if you see any without the little white pupae, squish or cut in half.

You may also want to spray your plants with BT to help keep the populations down -- healthy hornworms can create much damage in short periods.

Kevin

I wouldn't move the parasitized caterpillar away from the garden. Once the little pupal cases have formed, the caterpillar is very close to death, unable to do any further harm. We want those little braconid wasps in our garden.

That is the way all Tomato Hornworms should look, already parasitized by the Braconid Wasp.

Here is a link that might be useful: Image