They will shrivel up and die...they are food for the eggs that were implanted inside them by the wasp, hatched and then came to the surface as pupa. By the time you see the pupa (the white rice-like things) the worm has been a host for a while. It could have fallen off...sometimes they stay on the plant - brown and dried up.

i have been to so cal over the summer and raised hornworms there. you don't need to refrigerate them but you should keep them in a big terrarium with damp soil and they will be able to pupate there. make sure you keep them in a cool place (not too cold, just cool). also, they like to bury to pupate so i would recommend to keep them in a terrarium with a lot of soil as caterpillars so they can pupate under ground. thats better than burying them once they have pupated.

Susan, Thanks. It still isn't there, so I guess maybe it has pupated? It was very large. Based on the photos you linked, I think it likely was the Big Poplar sphinx. I looked closely at the plant. About 6" of it had been eaten, from the top down. Because there was not a huge amount of the plant eaten during the three days I was seeing that caterpillar on it, I do kinda think it must have been hanging around a few days as it prepared to pupate. I was wondering why it was in the same place on the same plant day after day, but it makes sense it might have been preparing to pupate as it was very large so definitely had been through several instars already. Bre, Even though I love tomatoes, I tolerate tomato hornworms. I just move them to other plants that I grow. Only very rarely has one damaged a tomato plant enough to cause me concern. While I don't grow all these other plants that Susan mentioned specifically for the hornworms, I just always make sure I have enough of them that the hornworms will have plenty to eat. Some years I have planted extra tomato plants in an out-of-the-way place where the hornworms can eat them all that they want, and if I have a tobacco hornworm damaging a tomato plant, I just move it to the extra tomato plants. About the only time they have ever damaged a plant enough to alarm me was with two potted brugmansias I overwintered in the garage. In early spring when nothing else they liked was growing, the first hornworms just about stripped the two brugmansias down to bare stems on days when I moved the brugmansias out of the garage into the sunlight. When we lived in town, I never had enough hornworms around to worry me. They are a lot more plentiful out here in our rural area than they were in town. It was my then young son who was fascinated with the hawkmoths that really caused me to pay attention to them. I was not necessarily thrilled to learn that the cool moths we enjoyed watching in the evening were the same creature that gobbled up my tomato plants in summer, but I got over it. I never really have many on my tomato plants anyway, and think that some of the companion plants I grow with tomatoes may have something to do with that. Susan, I grow every plant you listed.....and I wasn't even really trying to provide a food source for the hornworms. Well, let me say that a different way. I planted all those plants because I like them, but then I let many of them reseed and reproduce abundantly so that then there would be enough to feed the hornworms too. I also am growing garden huckleberries, Aunt Molly's Ground Cherries,regular no-name ground cherries and cape gooseberries, all of which are solanums, so I guess the hornworms will have even more stuff to feast upon should they choose to do so. Out in the pastures we have even more native solanums, so I would think there's abundant food for them this year. Dawn

I had a hornworm victory this year. While showing some friends around the garden, I spied a hawk moth on the back side of one of my tomato 2x2 supports. That dude was huge, like the size of a chickadee. After my friends left, I raced out there to catch him, but he was gone. Luckily for me, he was back the next morning, and I was able to do the deed. I had no way of knowing whether or not she had laid her eggs, though, but damned if I didn't find them a few days later. Tiny little hornworms, just hatching, and lots of unhatched eggs too, all on the same leaf. Of course they are all in hornworm heaven now. I can only hope these were the only eggs she laid, and that she didn't have any sisters who visited. I will be ready with my scissors just the same. But it taught me to be on the lookout for the huge ugly-a$$ moth early in the season.