Preventing Tomato Hornworms in the Garden
Big, fat, and green! These caterpillars can do a lot of damage to our summer crops—especially our precious tomatoes! Learn how to control tomato hornworms in your garden.
What Are Hornworms?
If you’ve ever grown tomatoes, chances are good that you’ve dealt with these green caterpillar pests. There are two main garden pest species, tomato hornworms, and tobacco hornworms, found in most regions of the U.S. and southern Canada. Both species can ruin your tomato crop in record time! They also feed on other plants in the Solanaceae (nightshade) family: eggplants, peppers, tobacco, and potatoes. They blend in quite easily with the green foliage and feed non-stop, creating spotty and chewed leaves and fruit.
Tomato (and tobacco) hornworms live according to the following life cycle:
- In late spring, large adult moths lay eggs on the undersides of foliage, which will hatch within a week. The adult moths are easily recognizable; they’re commonly called sphinx or hummingbird moths.
- Caterpillar larvae hatch in late spring and feed for 4 to 6 weeks before creating a cocoon and overwintering in their pupal state in the soil. If the weather is warm enough, larvae may burrow for as little as 2 to 3 weeks.
- Moths emerge in the spring and then lay eggs once again. In warmer climates, more than one generation a year may be possible.
How to Identify Tomato Hornworms
Hornworms can be up to 5 inches long—which can be quite a shock when you first come across one! They do the most damage in the caterpillar—or larval—stage. They are pale green with white and black markings, plus a horn-like protrusion stemming from their rear. (Don’t worry, they aren’t able to sting or bite!) The caterpillar also has eight V-shaped stripes on its green body. Tomato hornworms come from a mottled brown-gray moth (see picture, above).
The larvae blend in really well with the plant greenery. Just get used to a daily patrol, looking for hornworm eggs and small caterpillars. Here are some cues of infestations:
- Hornworms tend to start feeding from the top of the plant; look for chewed or missing leaves.
- Look closely at the TOP of your tomato leaves for dark green or black droppings left by the larvae feeding on the leaves. Then look at the underside of leaves, and you’ll likely find a hornworm.
- Look for stems missing some leaves and wilted leaves hanging down. You may find white cocoons and their hornworm hosts nearby.
Tomato vs. Tobacco Hornworms
There are a few species of hornworms that inhabit North American gardens, including tomato hornworms (Manduca quinquemaculata) and tobacco hornworms (Manduca sexta). Both species feed on common garden plants like tomatoes, potatoes, peppers, and eggplants. Here’s how to tell which caterpillar is which:
- Tobacco hornworms have parallel white stripes; tomato hornworms have white V–shaped markings.
- Tobacco hornworms have black spots lining each of their stripes; tomato hornworms do not.
- Tobacco hornworms have a red “horn” on their tail end; tomato hornworms have a black horn.
(It’s a tobacco hornworm! Notice the white stripes with dotted black lines and a red “horn.”)
Tomato Hornworm Damage
If you see leaves with large holes and severe defoliation, devoured flowers, and/or scarring on fruit surfaces, you might have tomato or tobacco hornworms. The fruit also may be damaged by sunscald because of the reduced foliage cover.
How to Get Rid of Tomato Hornworms
- Handpicking is an excellent tactic for control if you have the time and patience, or a small garden. The caterpillars are not dangerous and can neither sting nor bite. If you are squeamish about crushing these large insects, drop them into soapy water instead (or feed them to your chickens if you’ve got a flock).
- If the hornworm population or the area of your garden is too large, insecticides can be effective, though they should be a last resort. You can use the organic pesticide Bt (Bacillus thuringiensis), which is a bacterium that acts as a stomach poison on some larval insects (but doesn’t harm other plants or animals). It must be ingested by the caterpillars to be effective, and it must be reapplied to plant foliage after rain. Please check with your local Cooperative Extension for a list of approved insecticides in your area.
- Insecticidal soaps will also kill hornworms, but the pests need to come into direct contact with the substance.
How to Prevent Tomato Hornworms
- Till soil at the beginning and end of each gardening season to destroy overwintering larvae. Tillage has been shown to cause up to 90% mortality.
- Keep wasps around; a number of species are beneficial insects that feed on hornworms and act as a biological control. You may see hornworms with parasitic wasp larvae attached, which look like grains of rice (see picture above). These attacked hornworms will continue to feed for a little while, but will soon succumb to their hitchhikers, so it’s wise to leave them alone and let the wasps carry out their life cycle. Alternatively, remove infected hornworms and place them far away from your garden. This way, the wasps will still do their job, but the hornworm won’t continue to damage your crops.
- Other beneficial insects, like ladybugs and green lacewings, may feed on young hornworms or hornworm eggs.
- To keep hornworms away from your tomato plants next year, try interplanting dill or basil; marigolds are also an excellent companion plant.
See the Garden Pest and Disease Library for more information on common pest problems.
Do you have tomato hornworms? How do you handle them in the garden?
Catherine Boeckmann
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We had been wondering if we would get these in our little raised garden bed, and just found two (the first one with a shriek). I didn't know drowning was a way to deal with them, but I dropped them into the planter platter we used for a bird bath and that definitely did them in. And some happy birds apparently snagged them before I made it back to my window five minutes later. Circle of life. I've noticed sparrow flusters (clusters of flutterbombs) paying a lot of attention to my tomato plants lately (the past week). I'm wondering now if they have been feasting on eggs and fresh hatchlings...
Thanks to krp for the tip on biting. And thanks to Mr. Smesler for the tip on blacklights. I'll be trying that this evening!
You're a liar if you say they can't bite.
Whenever I get pick one off, it tries to bend up and bite me. I once got a bigger one that actually drew blood!!!!
If you want to say that they can't bite, I can assure you that they can AND WILL!!
I don't care what your entomology textbook may have told you. I know from experience for a fact that they DO bite.
My preferred method of dealing with them is to either take a long-nosed lighter and set their horned tail on fire, or strip off the leaf they are on and drop the whole thing in a bucket of water. Doesn't have to be soapy water, they will still drown
I can attest that I've seen these little beasts twice so far. I live in Colorado and we recently were hit by a huge swarm of moths which have thankfully died down now. I caught the first one eating my sage and basil, which I quickly removed and put it outside to eat some more wanted-to-remove plants. The second one came just today where I caught it in one of my pots with a celery stalk missing most of its leaves. It was also removed and humanely released into the weeds. Hopefully the rest if my plants, including my tomatoes, will be spared from this creature's attacks.
Can a tomato plant survive a hornworm attack? Mine were left with only a few leaves overnight, can they be saved?
Hi Lisa,
With only a few leaves left, chances are the plant cannot be saved. You could try leaving it and see if it starts to grow again, but the loss of leaves will most likely stunt the overall growth of the plant. Another option is to purchase a new transplant from a local nursery, as it’s not too late to try replanting. We hope this helps!
Today we found these little devils eating the plants. At least 6 on one small plant. I planted seeds that had already sprouted inside the tomato - as an experiment. Could the larve have been inside the tomato?
I've been gardening since the 1970's.
This year I had a problem with my rhubarb being eaten. It was a mystery and stunting the plant. Yesterday after finishing weeding I found a rather large tomato hornworm eating it. I had no idea that they ate rhubarb. I viciously killed the beastie. I felt better. I hope the rhubarb will start putting out taller stems.
The only reason I can come up with for this behavior is I didn't put out my tomatoes, peppers and eggplants until late and in beds far from the one I had last year. It was about 5' from where the tomatoes were last year. This years plants are in the opposite direction and at least 8' away.
I used to have problems with these pests until I planted Borage next to my tomatoes. The Borage plants have a prickly underside on their leaves and the Hornworms don’t like it. I haven’t had problems since. Make sure to start your Borage seeds as early in the spring as possible so they’re ready to plant with the tomatoes.
This is my 1st year with a raised vegetable garden. I have tomatos and eggplant. I have notice a few holes in my tomatos. I decided to spray my whole garden with Dawn dish soap and water in a small spray bottle. So far so good. No worms, no more holes in my tomatos. It has been raining for the last 4 days. I will check them again and spray if necessary. I really did not want to use pesticides. When I turn the garden this winter I may add something to the soil at that time. Hoping this simple trick works.
The tip I read about using a handheld UV light to finding hornworms on my tomato plants proved to be correct. They almost glow against the black color of the the leaves. Good stuff.
These weren't the big muthas but the juveniles, inch or two mostly. The black light works and makes it so much easier. I won a battle.
