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Tomato Caterpillars Identification and Guide

Updated on July 30, 2018
greenmind profile image

I am a writer, teacher, and parent. I have degrees in American history and human development, but insects are my true passion!

Tomato Hornworm Caterpillars

Caterpillars eating your tomatoes are most likely the larvae of a large group of moths, family Sphingidae. The group is distributed throughout the world, and some species are stunningly beautiful. But the caterpillars eating your tomatoes are not particularly beautiful, and they are exceptionally destructive. These are "tomato hornworms," and once these caterpillars get a grip on your plants, they can devour every leaf and immature fruit they find.

There are some effective ways to kill the caterpillars on your tomatoes, but good gardeners are thoughtful and proceed with caution. This guide will help you identify the caterpillars on your tomatoes to make sure that they're actually a serious threat. In some cases, you don't need to kill all the caterpillars on your tomato plants.

Is It a Tomato or a Tobacco Hornworm?

Big green caterpillars on your tomatoes are most likely a species of sphinx moth larvae. There are two closely related species in the genus Manduca, the tobacco and the tomato hornworm. The caterpillars are almost identical, and they both eat tomatoes, which can make telling them apart a little tricky. But from a gardener's point of view, the difference is moot -- there are great big green caterpillars on your tomato plant. Whether they're tomato hornworms or tobacco hornworms is not really the issue.

Manduca genus caterpillars are typically big and green with a curving "horn" on the tail end. For this reason, they are generally called 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.

Tobacco Hornworm: Manduca sexta

Source

Tomato Hornworm: Manduca quinquemaculata

Tomato Caterpillars Can Be Hard to Find

As big as they are, you would think that finding them would be easy, but it's not. 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.

Caterpillar Droppings Can Give Away Their Location

If you look under your tomato plants, you may see the droppings from the caterpillars up above. This means that you have a infestation, even if you can't yet see the caterpillars themselves. Caterpillar poop looks like little hand grenades. Some species fling their poop a few feet from the plant to throw predators off their trail, but tomato hornworms typically just let them drop. It's a good trick for finding them, because otherwise they blend in so well with the leaves you may never even see them.

Time-Lapse of a Tomato Hornworm Egg Developing and Hatching

Finding Them Can be Difficult, Despite Their Size

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.

Killing 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.

Natural Tomato Hornworm Caterpillar Control

The chief predator on tomato hornworms is a tiny wasp. This parasite -- actually a parasitoid, since true parasites rarely kill their host -- lands on the back of the caterpillar and glues on a batch of tiny eggs. These soon hatch out, and the baby wasp larvae, which are basically caterpillars themselves, burrow into the skin of the tomato hornworm. Once inside they begin to eat the fatty tissues and other non-essential parts of the caterpillar. The wasp larvae molt and grow larger, and after a couple of weeks they're full grown. The caterpillar, surprisingly, looks and acts normal while all this is happeneing, eating and growing more or less as usual. But when the larvae burrow back out and spin cocoons on the hornworm's back, it's all over. The caterpillar invariably dies; the little wasps hatch out and fly away to look for more hornworms.

Another Option: Soapy Water

Non-Toxic and Surprisingly Effective

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.

So what do you say -- Let them live or kill them all?

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    • greenmind profile imageAUTHOR

      GreenMind 

      5 weeks ago from USA

      Hi Amber -- Did you kill a moth? Because caterpillars don't lay eggs. They're they immature form of the moth that lays the eggs.

    • profile image

      Amber V 

      2 years ago

      I found one on what was my husband's jalepeno plant. It had eaten all the leaves and peppers seemingly overnight. Then, today, my daughter and I were checking on one of our barrels we have set up for bell peppers and my daughter spotted one near the top. I haven't found one on any other plants yet but I think we killed the mother that laid the eggs a few days ago!

    • profile image

      kelly c 

      2 years ago

      well I just found my first tomato caterpillar in my giant tomato patch I actually found tree big boys and a baby guess ill be caterpillar huntin this weekend I was wondering why my tomato plants were looking alittle depressed there being eatin alive

    • profile image

      anee 

      2 years ago

      I just don,t see that there so bad I like them and there are not ugly

    • profile image

      diane L. 

      2 years ago

      Once, many years ago, I had tobacco worms on my tomatoes Picked 'em of. Ugh. Just this morning, just THIS morning, I see only on two well apart plants, the top branches denuded. Maybe, my tomatoes have a chance since it looks like they just started. Pray. Thank you for insightfull information. D.

    • justramblin profile image

      justramblin 

      5 years ago

      I've found these on my tomato plants, too and the only way I discovered them was from the poop. Interesting to learn why it was so far from the little critter. They sure do eat and eat and eat. Good advice here. I'll try that soap method. The hawk moth is gorgeous and fun to watch at night.

    • verymary profile image

      Mary 

      5 years ago from Chicago area

      I hate those hornworms!!! They eat my husband's yummy homegrown tomatoes, which means less for me, which means grrrrr! Thanks for the info on these little pests.

    • profile image

      anonymous 

      5 years ago

      Very interesting about these caterpillars. Don't want the plants getting eaten.

    • CherylsArt profile image

      Cheryl Paton 

      5 years ago from West Virginia

      Thank you for the timely info. I like how you presented it. By the time I found the hornworm, the tiny wasp eggs were on it. I cut that part of the branch off and moved it away from the plant. I'll let nature do the rest. Thanks.

    • cathywoodosborn profile image

      cathywoodosborn 

      6 years ago

      I don't always kill them, but feed them to my chickens. Loved the video!

    • LaraineRoses profile image

      Laraine Sims 

      6 years ago from Lake Country, B.C.

      As you say, they are very hard to find! One thing I do is cut off the damaged part of the plant as I find them and then watch every day for more damage. I soon find the culprit. I drown them and then let the birds have them. Every time I kill one, I feel bad but ... they can do a lot of damage in a hurry. Angel blessings.

    • profile image

      anonymous 

      6 years ago

      I have to say this -- we grow tomatoes every year in our garden back home (we're in Brazil right now, though), and there was only one year where the tomato horn worms were so bad they were just decimating our harvest. And some of them had gotten really ridiculously huge, so big that a few of them, when I squashed them (really gross) actually made some kind of squealing noise. I thought I was going to puke. Luckily, they've never been that bad since then. Great lens!

    • JanezKranjski profile image

      JanezKranjski 

      6 years ago

      Shame they are so harmful, because I find them quite funny looking.

    • Virginia Allain profile image

      Virginia Allain 

      6 years ago from Central Florida

      I grew up in the country and food for the family comes first, so tomato hornworms weren't allowed to hang around. We did value nature and insects but had to save those tomatoes for canning and eating.

    • Lee Hansen profile image

      Lee Hansen 

      6 years ago from Vermont

      Tomato hornworms are definitely ugly and they destroy the plants so quickly. Love picking the off and letting them swim in a bucket of sudsy water.

    • LiteraryMind profile image

      Ellen Gregory 

      6 years ago from Connecticut, USA

      Interesting. I had an Aunt who when walking in the rows of tomato plants, would say "I smell a tomato worm" and sure enough there would be one. She insisted they smell.

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