That's a hornworm.

From the FAQ:

Tomato Hornworm - are 3-4" long green caterpillars with diagonal lines on sides, prominent horn on rear end. Eat foliage and may take bites out of green fruit. Tomato hornworms are the larvae of 2 large moths: the Hawkmoth and the Sphinx moth and overwinter in the soil in the pupal stage. Adult moths appear in late spring and lay single,
pearl colored eggs on the undersides of plant leaves that hatch in about a week. Larvae feed on foliage for about a month before they enter the soil and pupate. They can be difficult to spot as coloring matches plant. Look for them on the undersides of leaf-stripped branches. They can easily be hand-picked and destroyed or if infestation is severe, use Bt (Bacillius thuringiensis) dust. Braconid wasps will kill these caterpillars by implanting rice-like eggs on their backs and Trichogramma wasps parasitize the eggs.

I don't blame you for killing the caterpillars. Unless your plants were already huge, I doubt 2 plants could even support full development of 7 hornworms. One or two is okay, but not 7! I like the bugs, too. The moths are actually quite useful as pollinators of night-blooming plants.
Next year, try growing a few more tomatoes if you can. Hornworms have a place in nature and deserve to live as a species, but due to their size and tremendous appetite, they must be managed strategically, if some are to survive to complete their life cycle. Later, this winter, I will be offering FREE tomato seeds as well as a few other flowers just for butterfly and sphinx moth habitat. Look me up.

Thanks for your replies....

The funny thing is I didn't even PLANT tomatoes this year......I'm in the process of moving to another state in Sept. and have enough to do---while I planted every other year till now---and I really did want some fresh tomatoes, I just didn't have the time......Lo and behold, I looked out one day this spring and I saw about 20 tomato plants in different areas of my garden....Since I live alone, I've been "weeding out" all but 4...it was sooo fascinating to see them growing wild, and weathering themselves over the winter in zone 6...they were even growing in section of garden where I didn't plant last year!! Now that I got the taste for tomatos, I'll be darned if I'm going to let something else other than me eat them!! (big smile)
This morning I found one more worm on tomatos, and I actually "snipped it right in 1/2"---something I would never have the nerve to do before all this.......(felt great--kind of powerful, "taking back my plants!!) LOL!

Personally, I would have NEVER pulled 16 out of 20 volunteer tomato plants! It's really interesting to find out that tomatoes dropped off the plants, decay but their seed survives to grow into more big plants. If I do nothing, I will have a world full of volunteer plants, myself.

After you get moved and settled, keep posting here. I've got the seeds.

I have my tomatoes in pots on my deck-I used some of the old soil from last year and some Miricle Grow new garden soil. I am still getting worms-should I have used all new soil and gotten rid of the old soil since I had worms last year? Did the larva hatch from my old soil? Help!!

pick them bastards off and feed them to the chickens,chickens love them!make your rounds once in the morning once in the evening,no need to use any spray(save the spray for the white flies!)those worms can destroy a tomato plant in a blink,of course they deserve to live,just somewhere way away from the tomato garden!

I started 11 tomato plants from a great heirloom tomato I bought at the farmers market last year. I was horrified when I started finding tomato worms on my beautiful large plants, but tried keeping up with them by checking every morning and evening. As I hate to kill anything from nature,I clipped off the branch with the worm(s) and I kept them in large plastic bags and fed them the clippings as I prunned. When they were at the pupate stage I moved them away from my home so they could complete their cycle elsewhere. I don't know if this is the way to control them while keeping their cycle going or not? I just don't want them on my plants.
Anyway, I had to go in the hospital and was away for 3 weeks or so. I came home to 2 of the plants completely eaten, and huge worms, babies and eggs all over the plants. I just hope I can get control again!

Ninas Garden - It's admirable that you would go to that much trouble for the larvae stage of the Hawk Moth. I fully understand and agree that your actions were the right thing for you to do in your case.

However, I don't think there is any lack of Hornworms and Hawk Moths on the North American Continent. There are enough of them in the commercial tomato fields in Florida and Texas that never get zapped that will perpetuate the species for decades. So, for me, I will kill them as quick as I can before they destroy my food.

But, having said that, I would defend your right to have a different take on the subject.

Not only do they eat tomatos, but they are also attacking my Zuchinnis and Squash! HELLP!

When do they start to appear? Is it time already for them to start? (I am Zone 7 in NC)

I hate to say it, but the only way to control hornworms is to kill them outright or feed them to another animal (I used to give them to my pet hedgehogs). Just be sure that, before you feed them to a beloved pet, that the caterpillar is a Tomato Hornworm, not a Tobacco Hornworm... the latter has a bright red horn on its backside that delivers a powerful sting, and the former has a benign green horn. For heavy infestations, Dipel (aka Bacillus thuringiensis kurstaki) is a good control, and it's all natural, but hand-picking is always best ;-)

try them for fishing bait.catfish love them.

I like the scissors method. No need to worry about running out of hornworms. That would be like running out of houseflies.

EVERY year tomato worms cause me problems. I can never spot the buggers until they have done terrible damage. Also, they freak me out, I can't stand to touch them, so I always cut off the leaf or stem I find them on and throw them away.

This year I started spraying BT as a preventative (organic approved bacteria which only kills leaf eating caterpillars), and I haven't seen a single one. YAY BT!

I spray once per week just before sunset.

i just found a brown worm in one of my tomatoes. i have never seen this worm but have had the horn worm before. after closer look i found three more tomatoes that had holes in them. what kind of worm?,and what do i need to do

Every year I get tomato worms. This year I did not get a single worm. Difference: added coffee grounds on top of the soil. Could this be a deterrent? Hmm...maybe. Go to Starbucks and get your free used coffee grounds and try it yourself. Usually the worms are easy to spot when they get big or just by leaving results of their presence on my leaves. Haven't seen any evidence. Curious if this is a true deterrent.

shoeman, that sounds like it might be the tomato fruitworm, which burrows into the top of the fruit and makes a huge mess. It's the same pest as corn earworm, in case you grow corn too. Bt is a good solution for them.

If anyone feels like hunting hornworms, they glow green under blacklight. Go get an LED flashlight-type blacklight and go out at night, then shine it all over the plants and nab any glowing critters. It could be fun to do with kids. :)

I rarely have to exercise any control measures until September or maybe October, because I'm lucky enough to have several paper wasp nests in this area. I see them out doing their rounds, darting in and out of the tomato plants as they go along the rows 2-3 times a day... I see some small frass on the leaves, and a few holes, but never extensive damage. I don't see the worms themselves until the wasps near the end of their season in the fall (then I get some monsters, but the plants are big enough to cope). This variety of paper wasp is quite docile, and makes a good neighbor in the garden. :)

For those who don't have caterpillar-eating paper wasps, I generally recommend Bt, as it's harmless to people and other insects, and works quite well.

--Alison

WHAT DO I SPRAY THEM WITH??

Um, no, allowing them to pupate isn't going to control them. They will just mate and lay more eggs and create new worms for next year.

I found one the other day, just by accident. Now I'm checking every day. Instead of squishing, I will throw them on my patio. I have several birds that patrol my yard and it would be a great treat for them.

Don't waste your time spraying, most sprays anyway can't be used so close to harvest.....You need to pick them off---putting them out for birds is a good idea....had a few last year, googled it and read there is a hornet that breeds inside the hornworm and kills it for food---I looked again and there were tiny bumps on back of hornworm--definitely signs of the wasp, and the wasp killed it for me.....I would take them off, cut them in half or place where my bird feeders are in plain sight....If you don't want to physically remove the worm yourself, you might try cutting off the entire leaf it's on---they're big so easy targets...

Plants were fine yesterday (last night). Went to garden this am and my sweet 100 was almost destroyed. I found the culpret and with gloves, don't like the soft squishy feel, pulled it off and rubbed it out with my foot. Went back out this pm and found 7 more. I only have five plants and I will not let a catapiller eat my food source. Tired of factory canned tomatoes, to much sodium and sugar and I want to try canning this year.

Have two beautiful plants which were doing great; however, in one day I noticed two ugly, yet pretty, green tomato worms chomping away! I picked them off & thought I was done. I inspected both plants throughly, I thought. Next morning another pest. How do they hide so well? I don't want to use a chemical on my plants. I have at least eleven nice size tomotoes between the two plants almost ready to pick! Are these pests already on the the plants when you get them? It's my first time to grow tomatoes (I'm a little green like the worm).

I cut the whole leaf off and throw them in the road. This lets the cars do the work. You can easily find them, if you listen very closely. They make a clicking sound! Then, follow the sound. I do not feel sorry for them, or feel that they somehow deserve to be saved. They are a pest and I won't share my garden with them! I work too hard to let them eat up my beautiful plants.

The posterior horn or spike on ANY hornworm species does NOT sting, period! Whoever told Oragnic Manic that, is wrong. true tomato worms are by far, less common than tobacco worms. You all in Goergia and Florida may be overrun with them, but in texas and Oklahoma, they are NOT common and especially in south and central Oklahoma, numbers are rapidly declining.

No, Manduca hornworms do NOT eat squash or ANY cucurbits, brassicas or whatever. They eat nightshades and nightshades only--unless you have some goathead sticker plants ot transfer them to. There's a weird chemical in puncturevine that sustains them. Good. P'vine is a worse nuisance than the hornworms!

I am still wanting true TOMATO hornworms. These are the rare ones, have seven V-shaped stripes, black or green horn, green true legs and feel tough and leathery as opposed ot the baby-skin-soft tobacco worms.

I don't like to kill anything either, but I take exception to bugs that eat my plants. I read that if you till the soil in the spring, it will kill the pupae stage that overwintered in the soil. I'm going to try it next year. The coffee grounds sound interesting too!

teresa from Indiana, has the right idea! I'm in southwestern, MO. and gettin' lot of those critter right now...most of the ladies here do indeed drop them on the ground and stomp them flat! Good move ladies!

I decided to try container gardening this year and planted 20 or so tomato plants in containers with miracle grow garden soil. They were beautiful and grew quickly. One day I saw the leaves were being eaten. There were worms about 1/2 to 1 inch long and about the size of pencil lead and are gray to black and are found on the underside of the leaf.
I came to your site and found someone mixed 1 qt water, dish liquid(1 tesp.) and hot sauce. I sprayed it on the plants only where the leaves showed signs of damage which were at the bottom of the bush. I also picked off the worms that I could find. There were over a hundred. The next day, they were gone from the where I had sprayed but were highter up on the bushes where I did not pray, so if you try this, spray the whole bush real well. I also made the mistake of placing the pots close together so it made it easy for the worms to go from bush to bush. I have 2 bushes that are not with the others and they have no worms. I used tabasco sauce in my water. I know it has vinegar in it, but so far it has not damaged the plants. I go out each morning and afternoon to pick off the worms. I only found 3 today.

The Horn tomato worm eats until it is big as your middle finger then it rolls off the leaf, falls to the ground, pupae & come back as a moth & lays hundred of eggs.
Here in the South we get them in late May/June, then again in July then they will hibernate until Spring.
This year I have only found two, but I planted in two different places.

God save the Hornworms before they are on the Endangered Species List

The one in the lower right portion of your picture has parasitic wasp eggs on it; had you not killed it, it would have been devoured, and the cocoons would have developed into more wasps to eat more of your worms. Kill any worms by any method you choose, but any with white egg sacs on them should be isolated and allowed to be parasitized by the wasps.

Okay, so I am reading these posts and while many people are compassionate about their big huge tomato eating worms (I don't even kill spiders, and when I find them in the house I put them outside but come on) I pulled several off my plants and cut them in half with a big knife. And, kind of enjoyed it. Not pulling them off. I have been looking for these and all of a sudden (it seemed) there was poop around my two deck plants and eaten leaves and these stupid Hornworms. In a couple days. Eww, a couple were as big as my thumb. Will insecticides work at this late stage?

I don't kill spiders either, put them outside---thing is, unless you're using an organic insecticide, you're gonna kill the spiders on your tomato plants....I have webs on my tomato plants here and there that I've seen.....When I had a very bad infestation of the horn worms I picked them off and clipped the leaves off so they would fall on ground and I would cut them in half....luckily, I found some that had those hornet things on their backs which eat them from inside out....if you want to use an insecticide, I recommend Gardens Alive on the internet, they have catalog, I get all my bad stuff from them, they're pretty safe.....

Use bt for worms. It is very specific in what it targets, worms. They eat it, and get sick and die. Totally non toxic to two and four legged.
I'm not a pesti-fan, but bt is on my list.

I planted a tomato plant in a Topys-Turvy hanging gismo. The tomato plant is doing great, and is now quite large. Some of the leaves had small spots where it looks like it might have been eaten by some insect. On close inspection, I fourd a very tiny worm/catepiller about 1/4 inch long, white. I noticed that they were on more than a dozen of them on the leaves on the underside. If you touch them with a toothpick, they respond by dropping off the leaf. What are they, and should I be concerned?

I have found growing cabbage in six packs next to your crop keeps the guys away. You need to spray them, the cab, but keeps them away from crop.....