Tomato Caterpillar Identification and Control
How to Identify and Control Tomato Caterpillars
Did you find a giant caterpillar on your tomato plant? Big green caterpillars on your tomatoes are most likely a species of sphinx moth larvae. Tomato caterpillars are typically big and green with a curving "horn" on the tail end. For this reason, they are sometimes called tomato hornworms. These big, tomato-eating larvae grow up to be a big brown moth called a "hawk moth" because of their strong flight. Left alone, tomato caterpillars can eat your plants down to the stick. They eat the leaves and young fruit of tomato plants, and they eat a LOT. A few of these big boys can pretty much wipe out an entire tomato plant. These monsters grow to five inches long and weigh a ton, and all they do all day is eat tomato leaves and immature fruit. The horn protruding from their rear end gives them their name, but that horn is completely harmless, and so is the caterpillar. It cannot bite, sting, or otherwise harm you or anything else. Except for tomatoes.
I have studied insects for many years, and I am also a gardener with tomato plants that I would very much like to keep intact. There are several ways to control tomato caterpillars, including some that are natural caterpillar control methods and do not involve poisons or chemicals of any kind.
This article will help you identify and deal with the caterpillars eating your tomatoes!
Tomato Caterpillar Identification -- Big, Green, and HUNGRY
These big green worms begin life as a tiny egg laid in the early summer by the female hawk moth, Manduca quinquemaculata. There is little you can do to control tomato caterpillars in this early egg stage, and often you will have dozens of eggs laid on each plant. It's not until the caterpillars get big that you'll even notice the damage they do. But they get big FAST, and once you notice the damage you need to decide quickly what to do. It only takes a few of these caterpillars to really damage a cultivated tomato plant.
Tomato Caterpillars Are Hard to Find
Even though they're HUGE
It sounds strange, but it's true -- You can be looking straight at a tomato hornworm and not even see it. It's almost an optical illusion: the pale stripes on the insect's sides mimic the pale veins of tomato leaves, and the color is a precise match.
So take a close look at your tomato plants. Caterpillars almost always leave evidence: If there are caterpillars eating your tomato plants, you will see damage to the leaves. Look for fresh "gouges" taken out of the edges of the leaves. If the eaten edges are brown, the caterpillar has likely moved on a few days ago and could be anywhere on the plant. If the edges are green and fresh, the culprit is probably nearby. You are likely no more than a foot or two away from a very large caterpillar. They are silent, still, and beautifully camouflaged, and you will need to spend some time finding them.
Cool Insects from Panama
Tomato Caterpillar Identification -- Still-Life with Poop - Leaf Damage from Tomato Caterpillars
See the little "hand-grenades"? Those are caterpillar poops. Have a look on the ground around your plants. If you find them around your plants, you can be sure that someone is making them, and that someone is a big, fat, tomato-eating caterpillar.
Watch This Tomato Caterpillar As It Makes a Leaf Disappear!
Here's a tomato hornworm actually gobbling up a leaf. Notice how its jaws work sideways to bite through the leaf. Imagine this big green caterpillar eating and eating and eating -- more or less all of the time, since that's its only goal in life. How long before your plant is gone?
Let's Go Tomato Caterpillar Hunting!
Despite their size, tomato plant caterpillars are almost impossible to see among the leaves and stems of tomato plants. Their camouflage is so complete that you may find one, pick it off, and miss another half-dozen resting on the same branch. Keep going over places you think you have already searched. Where there is one, there are almost certainly more. Get other people involved in the effort if you can, since it is often true that other people will see ones you miss, and vice versa.
This is NOT a Monarch Butterfly
Tomato Caterpillar Identification -- Who Flung Poo? - Caterpillars eject their poops to avoid leaving a tell-tale trail
In this cool picture (public domain, of course, like all the photos here), you can see the big caterpillar poop-grenade being launched from the rear end of the caterpillar. Scientists think that tomato hornworms have evolved this behavior to throw hungry birds off their trail. If they fling their feces far enough away, they won't leave a big pile of dung under their position on the plant -- which a bird could learn to use to find them.
This Caterpillar Can't Hurt Your Tomatoes, But It Can Kill YOU
By Rodrigomorante (Own work) [Public domain], via Wikimedia Commons
Here's the Moth that the Tomato Hornworm Turns Into
Learn from your worms -- it is easy to raise tomato hornworm caterpillars to adults, and it could make an awesome science fair project for a child. The moths that tomato hornworm caterpillars eventually change into are pretty cool -- big brown and white bombers known as "hawkmoths" for their powerful, swooping flight. Since this stage of the insect's life is designed for mating and reproducing, these are the big moths that lay the big eggs. And as you may have guessed, the big eggs hatch into very hungry hornworms. And they start eating. Ah, the circle of life!
Time-Lapse of a Tomato Hornworm Egg Developing and Hatching
These Will Help You Identify Bugs All Summer - Identify Tomato Caterpillars and All Those Other Garden Bugs!
You need to be able to identify the bugs in your garden before you know what to do about them! Every bug in your garden has a weakness -- and you can find it with the help of a good insect guide book.
Controlling Tomato Caterpillars
Decide how to deal with your problem. If your plants are healthy and you have all the tomatoes you want, you should probably just live and let live. Birds drawn to your tomatoes may fill up on caterpillars instead, and that will save part of your harvest. Tomato hornworms are part of nature's grand plan, and they fill niches that you and I couldn't even guess at.
One Way to Get Rid of Tomato Caterpillars
Pick Them Off By Hand
This method is clean and natural, but time-consuming: Pick them off and smoosh them into the ground or your compost pile, where the scavengers and microorganisms that depend on dead animals can get their meal. Chemical insecticides are notoriously inadequate when dealing with tomato horn worms, and this method is both time-honored and, for some people, satisfying. My dad used to offer us kids a nickel for every hornworm we could find and kill. We could make several dollars some weeks -- maybe you could enlist the locals.
Poison Is NOT a Good Option for Caterpillars on Tomato Plants!
There are a few substances, like diatomaceous earth, that does help control horn worms -- but many will survive, and they will just keep on eating. More toxic substances are notoriously insufficient in dealing with horn worms in particular and caterpillars in general.
Tiny Wasps, However, ARE.
Natural Born Tomato Caterpillar Killers
Even if you don't do anything, Mother Nature might. There are several species of tiny wasps -- related to yellow jackets and paper wasps but smaller -- that attack the big tomato hornworm larvae. They lay their eggs on the caterpillar's skin and the tiny wasp larvae burrow into the fleshy parts of the caterpillar's body. The little wasp larvae eat the "extra" fat deposits of the caterpillar, avoiding vital organs, and then emerge to spin little white cocoons on the body of the caterpillar. That's what's going on in the photo -- a doomed caterpillar with dozens of parasitoid wasp cocoons on its body. Isn't nature grand?
Another Tomato Caterpillar Control Method
Try a Little Soapy Water
My mom swore by this method, though most sources recommend it for aphid infestations, not horn worms. Still, you have little to lose by trying this method, and you may kill off a few aphids in the bargain.
How to: simply fill up a spray bottle with warm water and about a teaspoon of plain dish detergent. Spray liberally on and around your tomato plants. The dilute mixture won't hurt your plants, but it may drive away the caterpillars.
What Do You Think?
You can choose to kill as many as you can get your hands on, or you can let nature take its course. After all, some farmers think of their crop as divided by thirds: one third for animals, one third for insects, one third for the table.