I rescued a tomato hornworm from skooshing today. Bob the caterpillar spent most of the day resting, but doesn’t seem interested in the fresh tomato limbs I have provided him with to feast upon. He isn’t really big enough to be in the wandering phase, he is only about 1’1/2’’ long and not particularly fat for the species either. He seems mostly interested in moping under the leaves and being grumpy. He has a warm place, correct host food, and has pooped, so I know he is not constipated. What gives?
God I haven’t seen tomato hornworms since I was a kid. I don’t know where they all went. Needless to say, I was less kind to them than you are.
I guess he is too small to molt, unless there are some really small species. Maybe they’d prefer to eat fresher plants; are you just breaking off branches? Potted might work better, but just give it time.
Edit: Wikipedia also says there are tobacco hornworms and not to confuse them. You might want to compare the descriptions there.
Does he have direct sunlight? He’s evolved to live by hiding under tomato leaves as a response to bright July sunlight, so maybe you’ve confused him by bringing him indoors and putting him the mere ambient light available in the average human dwelling.
Also, how much space does he have to wander around it, i.e. what kind of container is he in? He’s used to the wide-open spaces in a tomato patch, so maybe if you’ve got him in a mayonnaise jar or something, he’s just not comfortable.
Or maybe he won’t eat dead branches, and even freshly picked leaves have, by definition, begun to die. Maybe he needs to have that fresh spurt of juice to be happy.
Or maybe he’s just still in shock. Give him a day or so.
Or maybe he just eats slower than you expect.
Or maybe you got yourself the one dysfunctional tomato hornworm in your garden, the caterpillar equivalent of the emo adolescent moodily staring at the walls.
That’s all I got.
Let us know if he pupates and turns into a moth, because, honestly, I’ve never heard of anyone raising a tomato hornworm/sphinx moth in captivity before. I mean, why? You don’t even get a bee-you-tifull butterfly out of it; they’re one ugly mutha, comin and goin… 
Um, you could but why would you?
I accidentally stepped on one once…in my bare feet. ewwwww.
I think he’s interesting, and I rather like the sphinx moth he will turn into.
Currently Bob is hanging out in 1 gallon container with freshly picked tomato limbs. He did get active at night, but doesn’t seem to have eaten. I’m going to offer him some dirt in case he’s just a runt and really is in the wandering phase.
It’s on a hunger strike in protest of it’s wrongful imprisonment, duh. Does PETA have an Amnesty wing?
You really have no idea how much tomato foliage it will need to eat to make it to the cocoon stage. One will strip plant after plant, and eat the stems even. You’ll need to sacrifice multiple large plants. In case you still want to do this, cage in a plant and put it on the plant.
Maybe a pack of Parliaments will give him his appetite back.