It will turn into a really cool moth called a hawkmoth or "hummingbird moth." The species is tobacco hornworm, Manduca sexta. It's a sphinx. Full grown, the cat may be upward to 4" long.
No need to get rid of it, but I still recommend captive rearing for 2 rasons. First, to preserve it and make sure it won't get a parasite. Second, is so YOU can choose which leaves/stems to cull to feed it.

You need to comb your plants. You may find at least 2 more like it. Good luck!

Thanks, Tomato Worm. Great info.

Better look for more of the little guys. If you don't, some day you will go into your garden and you will find defoliation like you have never imagined. You will decide not to "sucker" your plants anymore because you wonder how much damage these cute little worms can do. Check once in the morning and once in the evening, if you have time. Don't destroy the ones with white cylinders on them. The cylinders are a parisitic wasp that consumes the worm. Mother nature has a way to keep things in balance, no matter how hard we try to change things. If raising butterflies is your thing you have a big one. Paul.

Tomato Worm59;

How does one 'raise' these worms?

What type container do you put them in, and how do you know when to turn them loose?

I just picked 10 of them off our tomato plants this morning, I put them in a plastic container with slits on the top, bottom and sides (it was origanially used for doughnuts). I gave the worms some fresh cut tomatoe stems/leaves; now what???? :>)

Just keep feeding them. They will eat 4x their weight in leaves and tender stems. These sphinx cats actually eat more and faster than many other sphinxes or even giant silk moths. The important thing beside enough food, is keeping their container clean! The Manduca larvae eat so fast, that their droppings are also quite "wet" and these will mold quickly and are potentially hazardous for the cats, just as walking in their own manure is bad for other animals.

When the caterpillars reach maximum size [usually about 3-1/2"] they will eat a lot, then suddenly stop eating and just start wandering around. It will be looking for a place to pupate. This is when they need to be placed in a container with moist, but not wet, dirt. In a day or so, it will bury itself.

For the health of your caterpillars, be sure to look them over real well. You can see the spiracles. Those are normal and will be red or black, depending on the hornworm species. However, if you see dark spots in other places on the cat's body, isolate it, to see if it lives. dark spots can be disease or sign of parasites. Hornworms should stay green, not turn black. That's a viral disease and kills a lot of captive and wild cats. Believe me, "black death" can wipe out a whole brood. There's been lots of discussions on this topic on the butterfly garden forum.

I like to use at least 1 spare container for each group of cats. This way, all the cats from each container can be transferred, their own one cleaned and kept for either the next day or just working down a line of several conainers. I use a mild bleach water solution and make sure the container is thoroughly dried before use.

Good luck. I wish I had 10 hornworms!

Well, my tobacco worms just showed up.

One i spotted by chance....and inch long...I'll give any of these to chickens, but save the bigger ones, later, to pupate, Tomato Worm....

Aww, you'd feed a tiny baby 1" baccer worm to a chicken? Just enough to make that bird want more! I've never found one that small. Maybe you have some spare leaves for it. They do grow fast.

Oh gosh, no....if this is any indication, I'll find about 100 of them this year, all told...I have 350 plants. I don't want to try to raise too many of them, for too long...don't they tend to get sick in captivity?
Yeah....i rarely find them until at least 2 inches.

Cat, I'm glad to hear the sphinx is doing so well in your region. Sounds like you have food aplenty to rear at least 100 of them. The biggest question is, do you have the time? I had at least another 60 or so plants I could have set out had I the time and energy. I got a full-time job just after I began my planting. Needless to say, the tomatoes largely went neglected as it got hotter and hotter, sapping all my strength just enduring my outdoor work.
I hope to do it all over again next year, providing not only fresh tomatoes for family and friends, but to propagate hand-pollinated pure seeds and of course, provide habitat for both species of the nightshade-eating Manducas.
Captive-rearing can be somewhat hazardous for the cats. They must be kept in a CLEAN environment. crawling around in their own waste is definitely a no-no. It's been linked to viral and bacterial infections, just as wallowing in their own waste could be fatal for your chickens. Rearing hornworms and other cats will give them an advantage over predators and parasites. I find the big caterpillars of all kinds, literally as much fun to rear and by far, less smelly, than baby poultry or gamebirds!

I've got time for the plants, but not 100 cats.

I was thinking of raising 20...hoping to get 12 to pupation for you. Probably all i can handle keeping clean and all....what do you think? (I'd rather feed them to my chickens than have them just fade from disease.)

I've never seen parasite eggs or anything. Don't know if birds get them....my plants are huge and dense, so they'll hide easily.

The extension says they don't overwinter here...it's too cold...what do you think?

It's hard to tell. Even if they don't overwinter, the wandering moths could migrate in. Sphinx are capable of long-distance flight. Still, I do know Cecropia and other moths are also found in Maine. No, they are relatively poor flyers and will not go so far. Their cats survive as pupae in cocoons on tree limbs. Why can't a sphinx pupa survive, buried in the ground? Hmmm.