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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Very jnformative, thank you.
I've had whole collard plants eaten and kale that was chewed this year and could not find anything eating them, just some black "poop balls" left behind. Today I notice a tomato plant completely bare of its leaves and found this huge hornworm covered in the wasp larvae. My question is, Is it safe to eat greens that have been chewed by these creatures?
It should be OK; we haven’t heard about any cautions regarding hornworms affecting edibility of crops in that respect. After harvesting, cut out any damaged areas and throw out any rotten leaves. Then wash the greens thoroughly just before eating, using cool running tap water. You can blot the leaves dry with a paper towel or use a salad spinner. Be sure that your hands and any utensils/tools and food preparation surfaces are clean. (It is recommended that hands are washed for at least 20 seconds with soap and warm water before handling food.)
i have what i thought was the cabbagelooper doing damage to my plants but now i'm not so sure. i've been collecting the cocoons at various stages and have come across many that look like a worm encasing hundreds of eggs. could this be a way of reproduction for them that i'm unaware of?
please advise
Are these cocoons on a caterpillar? See the photo of the tomato hornworm with the braconid wasp cocoons above - these are one insect per cocoon. Braconid wasps are parasites of the hornworm. If you see these on a worm, leave them be. The hatching wasp larvae will take care of the hornworm pest.
The eggs of a cabbage looper are laid with no protective covering on leaves, singly or in small clusters, and are whitish yellow to green. Each pupa is encased in a thin white cocoon under foliage; the pupa itself is green, then turns brown to black, before transforming to a moth. A few insects make egg cases, such as praying mantids and spiders (egg sacs), which contain many eggs. A common tomato pest that might do this, though, does not come to mind at the moment.
Don't like worms to see in my garden . Thanks for all the Infos.
I have this worm eating my tomato plants,but it is black with gold v-stripes. What should I do with it
This sounds more like an armyworm. Besides handpicking, you could try applying the natural bacterium Bacillus thuringiensis (Bt) for control. Talk to your local garden store.
We're under attack!!! Never one to be afraid or grossed out by bugs, but these are no bugs! They're creatures! We never had them before & planted our tomatos & peppers in containers with new soil. We're checking daily & removing them regularly. Also spraying with soapy water. Lots of great info on your site & now that we know about the wasp eggs & the villain moth, we'll be on the hunt. Thanks!
I found and removed one large hornworm from my tomato plants today. This is the first time I have ever seen one. Can they be found in isolation, or do I probably have more?
