Identifying the Caterpillars Eating Your Tomatoes
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 hornworm caterpillar.
The scientific name for these big boys is Manduca quinquemaculata, and they are the larval form of a big brown moth known as a "hawkmoth" for its powerful, swooping flight. Chances are good that you will never encounter the moth, since it hides during the day and is pretty inconspicuous despite its size.
But if you grow tomatoes, you are almost certainly familiar with its immature forms. Read on for some information and advice about what to do with those big green caterpillars!
How to Identify a Hornworm Caterpillar
- Usually pale leaf green in color, but sometimes black
- Seven V-shaped white stripes along the side
- Eight black and yellow spiracles on each side of the body (look like eyes)
- Dark blue or black horn on its tail
- Grow as large as 4 inches long
- You'll probably find them near tomato, pepper, or eggplant, since that's what they like to eat.
How Can I Tell if Caterpillars Are Eating My Tomatoes?
- First, 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.
- Then check for young tomatoes and leaves 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 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.
- Check the undersides of the lowest branches, near the main stalk. They like to hide there.
- 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.
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.
So You've Identified Your Caterpillars as Tomato Hornworms—Now What?
Let's say you do find a few fat green hornworms gobbling up your tomatoes. Now it's time to deal with the problem. You may simply decide to live and let live, and really, unless you rely on your tomatoes to survive, why not share the wealth a little? Hornworms will eat a few but overall they are usually not a huge problem, much less serious than aphids or disease. Also, the birds who would usually peck away at your tomatoes will fill up on fat green caterpillars instead. Consider making them part of an educational experience. They are pretty easy to raise—they eat tomatoes, duh—and after they pupate, they turn into big brown moths, which is pretty cool if you have kids. So don't just assume that your hornworm problem is real ALL that serious. Has anyone ever said, "wow, I really don't have enough tomatoes from my garden this year"?
But okay, let's say you want those hornworms gone. Here are a few options.
How to Get Rid of Tomato Caterpillars
Method #1: By Hand
The first method to eliminate them is to physically pick them off the plant. This is labor-intensive, but work like this is, I believe, the reason that children were invented. Children and pocket change: offer the neighborhood scamps a dime 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?
Method #2: Organic Solutions
The half-way step between removing them with your bare hands and plain old poison is insect soap or dust. There are several recipes for this online, and they usually affordable and generally fairly effective. They work by blocking the spiracles (the holes along the side of the body that the insect uses to breathe).
Another product that I have used with success is pure cedar oil. It's safe, effective, and it smells good too! It's been used as an insect repellant for eons. If you're determined not to use chemical insecticides, cedar oil may well be an answer for you.
Ladybugs, green lacewings, and common wasps are its natural predators. They can also be reduced by planting marigold close by.
Method #3: Poison
Okay, if you must, there are compounds available at the hardware store or garden center that may kill off your tomato hornworm population for good. You can research these on your own. There are various kinds and substances on the market, and they all claim to be safe, and maybe they are, but they can't be as safe as paying a bunch of kids pocket change to pick caterpillars off your plants is.
To Poison or Not to Poison?
Would you ever decide to use poison or chemicals to control tomato hornworms?
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.
Learn how to identify these stinging caterpillars at Guide to Stinging Caterpillars of North America.
What's Up With the 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.