Let’s talk hornworms. Not very many things in my garden give me the heebie-jeebies, but these caterpillars do because they are just so big. I am getting over it – slowly – but I figure all of you new gardeners deserve fair warning. there are two varieties of hornworms – tomato and tobacco. They both feast on your tomato plants (as well as pepper, potato and eggplant).
Leaves eaten 
“skid marks” on tomatoes
Signs and Symptoms… If you notice skid marks and holes on your tomatoes, and poop on tomatoes, and leaves missing from your plant, wilting leaves in a specific spot, chances are good you have a hornworm eating all of your hard work. There are a few differences between a tobacco and tomato hornworm (number of strips, black margins on markings, color of horn – tobacco have a red horn, tomato have a blue horn), but they both do the same amount of damage. For someone who has a small garden, they can destroy your tomato plants in just a few days. I like to maintain my garden without pesticides, so yes, this does create a little more effort on my end.
Solution: To treat without chemicals, you just have to pick them off (use tweezers if you must) and kill them. My kids are infatuated with them and love to search for them and smoosh them for me. Because of their color and markings, they can be difficult to spot unless you are up close and personal with your plants. Let me share an awesome secret with you… A blacklight flashlight, when used at night will illuminate these critters, making them very visible!!!
Hornworms have about a 4 week lifespan (so luckily it’s not an issue all season long) before they burrow into the ground until next year, where they will turn into a big moth (Hummingbird moth) and lay more eggs. You can search for eggs on the underside of leaves, but search quick because they hatch in less than a week!
Tip: Hornworms sometimes ‘click.’ If you shake a plant and hear the click, you may be able to locate the offender.
Prevention: The best ways to prevent issues include rototilling your beds before planting (to break up the pupae or bury it deep enough to kill it), planting companion plants with or near tomatoes the following year, and rotating where you plant your tomatoes each year. Generally, a 3 year cycle is suggested for all crops.
And no, the hornworms don’t actually sting with their horn. They are harmless and can be picked off by hand. If damage done to your plant is on the minimal side, it will recover just fine.