So how to spot a hornworm: there are 2 telltale signs hornworms have taken up residence in your tomatoes. 1 is leaf damage, and the other is frass (super fancy name for poop).
Frass (or poop) looks like wee little grenades. It can be black or green. There may be a little or a lot, depending on how long your hornworm has been noshing on your plants.
Usually, if you look straight up above the frass, you will see the hornworm. However, the one on this plant has been moving around a lot so I actually had to hunt him down.
It takes a LOT of hunting sometimes to find them. They blend it very very well with a tomato plant, making them difficult to find. Peek-a-boo! I seeee you!
Now, if you're a brave little toaster, you can pull him off of the leaves. They don't bite, and the horn is fake. But, if you are a giant wuss like me you have a couple of options:
1. Remove the leaf the hornworm is on, taking the hornworm with it.
2. Enlist a child to pull the hornworms off your plants, and pay them a dime for every worm they get.
In this case, I took the leaf with the hornworm on it. My son usually gets them for me, though.
*Shudder* That one is still a baby, believe it or not. They can get 4+" long and will eventually turn into a moth.
You can drop the whole thing in a bucket of soapy water as hornworms aren't great swimmers. You can squish them, but they make a bit of a mess because they're so big. If you're lucky enough to have chickens, they really enjoy them as a tasty snack.
I wipe the frass of the leaves so if I don't think there is another worm on the plant at a later date. I check my plants at least twice a day.
You can use Bt (Bacillus thuringiensis kurstaki) ton control the population, which is safe for all critters that aren't a caterpillar.