I'm a life-long naturalist and citizen scientist with a deep and abiding curiosity about the natural world.
Tomato Caterpillars—What Are They?
Do you have big green caterpillars on your tomato plants? That's a sure sign that your garden is playing unwilling host to one of the most common tomato pests in North America, the tomato hornworm caterpillar.
The scientific name for this insect is Manduca quinquemaculata. They are the larval form of a big brown moth known as a "hawkmoth" for its powerful, swooping flight. You will likely never encounter the adult moth, since it hides during the day and is pretty inconspicuous despite its size, but if you grow tomatoes, then you have probably come across the big green caterpillar of this species at one time or another.
This guide will help you identify the big green caterpillars that are eating your tomato plants, and also offer some ideas for controlling the damage.
How to Identify a Hornworm Caterpillar
- Leaf-green in color. This shade of green blends in perfectly with the leaves of your taomato plant, so even though they can be huge, they can also be very hard to see, even when you look very closely.
- Eight V-shaped white stripes along the side. These markings match the veins on the leaves of the tomato plant. Added to the green background color, they give the tomato hornworm one the best camouflage jobs in all of nature.
- Eight black and yellow spiracles on each side of the body. These are tiny airholes, and it's how the caterpillar breathes. If you clog them up, the caterpillar dies, and this is one way to control them (more on this in a bit).
- Curved horn on the tail-end. This is called a "caudal horn," and it often has a red, yellow, or blue color to it. This of course if how the tomato hornworm gets its common name. The horn looks scary, and it's supposed to, but it's not a stinger or even sharp. It's just for show -- the tomato hornworm is completely defenseless against a predator as big as you!
- Grow as large as 4 inches long, and this is not a skinny four inches, either. They're fat and heavy. If you hold one in your hands you'll be surprised at how massive they are. They got that way by eating one thing and one thing only: lots and lots of tomato leaves and fruit.
- Specific to tomatoes, but will also occasionally eat eggplant, peppers, and related vines.
How Can I Tell if Caterpillars Are Eating My Tomatoes?
- Examine your plants. The first sign of a caterpillar infestation is missing leaves. These guys can eat a leaf right down to the stem, and if enough of them attack a plant they can turn it into a cluster of bare green stems and stalks. It's probably the big green larva of the hawkmoth, and once you have them, it can be hard to get rid of them.
- Check for young tomatoes that have been partly (or completely) eaten. If you have leaves with big chunks missing, and baby tomatoes with even bigger chunks eaten away, you probably have hornworms in your garden.
- If you still don't see evidence, have a look around the ground under your plants. You are looking for poop, and these big caterpillars make big poops. They look a little like tiny hand-grenades. A pile of these under a tomato plant means someone up above is doing some serious eating.
- Where there's one, there's more. If your eyes are sharp and you do find one munching away on a leaf, don't stop! Keep looking—where there is one, there is almost certainly a whole bunch more close by.
- They hide in plain sight. Even when you know what you're looking for, these big caterpillars can be hard to find. They are unbelievably well-camouflaged on the bright green leaves, and the little slanted marks on their sides blends perfectly with the angled veins of the tomato plant leaves. So when you look, you may find some, but you may not—they are truly well-adapted to evade discovery by predators, which you are now.
Tomato Caterpillar Control Option 1: Pick Them Off by Hand
The first method to eliminate them is to physically pick them off the plant. This is labor-intensive, but it's perfect for the young ones in your family or neighborhood -- when I was a kid it was a dime per caterpillar, and we made enough to buy a week's worth of candy. Offer the neighborhood scamps a a small bounty for every hornworm corpse they bring to you, and there's a pretty good chance your caterpillar problem will be over. You might be down a few dollars, but it's a better deal than paying for store-bought insecticide that may or may not work.
The drawback to this method is the same reason that hornworms and other prey insects are not extinct: it's really impossible to kill every member of a population, unless you also destroy their habitat (predator animals don't do that, while humans are sadly very good at). So yes, some caterpillars will survive and keep munching on your plants. But the problem will be a lot less serious—maybe you could even live with it?
Tomato Caterpillar Control Option 2: Diatomaceous Earth
This product is not a poison or a chemical of any kind, and the way it works is quite interesting. Diatomaceous Earth is refined and filtered dirt that contains the silica shells of millions of tiny organisms called diatoms. Under a microscope, a pile of these empty shells looks just like broken glass -- which it basically is, since glass is made of the same material. When an insect crawls across diatomaceous earth, the jagged shells damage the insect's outer layer, and it dies.
This material has been used as an insecticide for a century. It's safe for humans (although you're advised to wear a mask when applying it), and even comes in a "food grade" form that some people take as a supplement.
Best of all, there are no chemicals to get in the soil or end up in your food. Rain washes the dust away and you have taken care of your pest problem organically.
Diatomaceous Earth for Pest Control
To Poison or Not to Poison?
Are Hornworm Caterpillars Dangerous?
Although the tomato hornworm does have what looks like a stinger coming out of its tail, it's completely harmless. There are some other species, though, that are venomous and can give you a pretty nasty sting if you touch them or brush up against them. Handling caterpillars is fine if you know which one you're dealing with, but otherwise it's best to use gloves or avoid letting the caterpillar contact your skin, especially if it's furry or has spines.
Why Does It Have a Horn?
The curved tail or horn on the hornworms's rump is not a stinger, though scientists think it may look enough like one to provide protection to the caterpillar. There is no sting, or even a sharp tip to the horn, so its use as a protective device is debatable. It has also been suggested that the tail resembles a snake's tongue, or that it draws attention to the back end, sparing the head of the insect from attack.
Wanda on June 26, 2020:
Have a black looking small Caterpillar eating my tomatoes. Any help to rid these pesky things.
Teresa on July 30, 2019:
easy to find the tomato HORNWORM at night with a black light. Makes them glow like a lightning bug. I check my tomatoes, peppers and potatoes.
Nancy Peters on September 21, 2018:
thank you so much. i just found a hornworm on one of my two tomato plants. Interesting critter but I have too few tomatoes to share with it. Fun reading about it tho'
C Faith on August 27, 2018:
I have used Marigolds for years to keep rabbits out of my garden. A side benefit of this practice is that it helps repel tobacco horn worm caterpillars. They also make an attractive border to vegetable gardens.
clntrigger on August 07, 2018:
Before you go killing all those bad green bugs on your tomatoes , look around your yard. !!!!It is probably your fault they are there. yOU must have other beautiful plants and flowers around. these attract butterlies and moths. Mostly what you are seeing are a type of sphinc moths. Look up on the internet. there are several kinds depending on your area. It would be a better idea to have a tomato plant dedicated to these bad guys than killing off the whole population. Remember you have the plants that are attracting them. THE NET WIll tell you how many eggs to look for and how many days to hatch. then you will have moths at night in your garden. They are easy to take from one plant and put on another. L love my tomatoes too but I ALso like the nature they attract. SO put the bug spray away and get educated before eliminating everything you dont understand.
Fred's Bughouse (author) from near the Equator on July 07, 2018:
@Kwame I can understand your position!
Kwame Dankyi on June 02, 2018:
One tomato seedling well grown from the garden center can cost about $3 to $4 per plant. You bought 10 of those and good compost to grow it. I love my tomatoes that is why I am applying all these efforts and money. So I am not sharing one leaf with a grubber. Please advise. If they will develop into beautiful humming birds then fine but moths? no way!
Phil on April 14, 2018:
Moths lay their eggs UNDER the leaf of the tomato plants and they is why you do not see them until they have begun chewing your tomato plants to death. These litle green base tards double in size every other day, so you need to keep an eye on your tomato plants every day. I cure my problem by covering my tomato plants with some fine mesh fbaric that allows light, air and water to penetrate the material. It cost a few bucks but I cannot watch my garden 24/7 and if you buy a decent fabric it will last a few years so you can sue it over and over again. I garden organically but I do not see the point of spraying neem or orange oil on my plants all the time especially since it rains often here in the Houston area. The fine mesh netting does it all for me and tomatoes are self pollinating so you don't have to worry about that. However, I have increased my yield once the flowers appear I will take an old electric toothbrush and brush on the top of the flowers to simulate a bee and the pollen will drop and help set fruit. I do this either early in the morning or at sunset. You can also shake or thumb the leaves to loosn the pollen but the tooth brush is more useful and doesn't knock the flowers off.
Chris Grina on September 15, 2017:
Every time I grow tomatoes, the horn worms seem to appear out of nowhere, now they are in my vineyard...is that normal?
Judith Maier on August 26, 2017:
My deck is about 15 feet off the ground. I have several tomato plants in pots. I had these droppings on my deck which looked like little pellets just below one of the plants. I would wash the deck down every morning and then they would reappear the next day. Today the droppings happened while we were right there and one of our guests spotted the caterpillar. It was unbelievable the way that it blended right into the plant. This guy was pretty big. Should I expect more? Your article was a big help in identifying this caterpillar.
Gaia on August 26, 2017:
Thanx for article!
What to do with those tomatoes that just had worm eggs on them and after washing there are spots on them where eggs where?But otherwise tomato looks decent.Can I eat such tomato?
Jean Bailey on August 25, 2017:
I think that I found a tomato hornworm on a leaf of one of my pepper plants this morning. It was covered with small white oval attachments that from your article are probably wasp eggs. I took pictures but I guess I cant post them. I would like to be able to verify my find but since the damage to a few of my tomatoes is as pictured here I have to assume that is what I have.
TinaHutto on August 10, 2017:
Luckily I haven't had a problem with the tomato hornedworm this year but I have little black worms this year with a yellowish stripe..anyone know what kind of worm it is and how to wipe it out before it wipes out my crop?
Marlane Renner on August 05, 2017:
I have marigold plants in a container right next to the container tomato plants, and guess what? I've got the hornworm caterpillars! They are beautiful, but boy, do they like to eat!
Nina on July 29, 2017:
They already ate all of my tomato plants...I only had 2 of them. So I guess they get to live.
Theresa on September 11, 2016:
The eggs are wasp eggs. when they hatch they will kill the caterpillar. They are a natural way to get rid of them.
erinbliss on September 10, 2016:
OMG, just found one this morning! AND it has eggs hanging off it like crazy. In fact the eggs are how I found it. I wish I could post a photo.
joe on August 28, 2016:
Wasp eggs. They eat the worms.
tina on August 21, 2016:
what are those little white things. Eggs!!!
Don Cooper, DC on August 14, 2016:
Simply plant marigolds near your tomatoes. Presto! No horn worms will appear.
George on August 05, 2016:
I was going to blame the dozen or so squirrels for munching my few tomatoes for moisture until I discovered the beautiful hornworm. Your suggestions are great. Thanks
Pamela Dapples from Just Arizona Now on August 05, 2014:
Great hub you've done here and you're braver than me -- using close-ups of these critters. I couldn't use close-up photos. Voting way up and sharing. T'is the season for the critters.
Susan on September 23, 2013:
My Hornworms are feeding on the poisonous Angel Trumpet plant. Holy moly, how toxic are these moths going to be to anything that eats them.
Cindy A Johnson from Sevierville, TN on September 10, 2013:
I encountered my first ever tomato hornworm today and was thankful for your hub for more information. While certainly destructive, the caterpillar is quite beautiful. Thanks for enlightening me!
Sharfire on August 09, 2012:
I'm going to try the water, dish soap, baking soda and cayenne pepper spray and see if this will turn off those caterpillars.