That is a tomato worm. As they get bigger, they develop a ferocious appetite. They hide at the bottom of your tomato vines under the leaves during the day and come out to feed at night. My grandmother used an old fashion remedy to tomato worms by using sulfur dust. Sulfur dust will get rid of them. But I go one step further. Go out at night with a flash light and pick them off. Use your cutters if you like and cut them in half to kill. You can find them a lot easier at night while they are feeding. A dead give-away is that they leave large piles a black droppings right under where they are. Look on the ground for these droppings then look up above into the vine for their location and kill, kill, kill!

Lily Miller sells sulfur dust in a shake-can for killing tomato worms, among other things. You just powder your leaves with it. The worms will find it and die. The stinger-like looking 'horn" is part of their camouflage. It is not really a stinger. It makes them blend in with the plant and look like a stem with a thorn on it.

When they get to the size that you are showing in your picture, then can devastate your tomato vines in one night. So get your flashlight and get them off your vines tonight! I have found that by using a diligent program of night time hunting, I did not have to use the sulfur dust.

When they are a moth they look like a hawk moth.

This is definitely a tomato hornworm because I have seen these on my past tomato plants and ground cherry plants and these suckers gets really big so I just used skewers as chopsticks and picked them up then feed it to my chickens!

green horned caterpillars,

That is a hornworm.

We found this bug had been eating our plants in our garden. Tomatoes, leaves, even little nibbles of some peppers. We live in Ohio and we've never seen this bug before. Does anybody happen to know what it could be? Also, it has a little purple stinger on the back of it and it's upside down in this picture. There were two, maybe more, that we found. Please help, thanks!