Friday, July 22, 2011

Tobacco Hornworm

I wanted to bring you an article written by one of my fellow Master Gardeners in South Carolina.  After reading Daricia's article about the Hornworms in her Charlotte Garden, I thought Ann's article would be a good companion to the other posting. 
The following article originally appeared in our MG newsletter. 

Tobacco Hornworm

By Ann Barklow
I often think of myself as an amateur research scientist when I am in the garden. When I see anything moving, I move in closer for inspection. For my research, I am never far from my 10X hand lens, laptop computer or iPhone, and camera.
Today I spotted a tobacco hornworm. I found it on my tomato plants and for obvious reasons; I was tempted to call it a tomato hornworm. You can distinguish the two by their markings. The tobacco hornworm has straight white lines like a cigarette pictured below and the tomato hornworm has “V” line markings like “vine” ripened tomatoes.

Tobacco Hornworm

If you have these large invaders in your garden in South Carolina it is most likely the tobacco hornworm. Tobacco, tomatoes, potatoes, eggplant and peppers are all in the Solanaceae family and tobacco hornworms will feed on all of them but seems to prefer tomatoes in my garden. Of course I’m not growing tobacco so I can’t speak to that.
The name hornworm can confuse you too. They do have a horn but they are a caterpillar not a worm because they are the larva of a moth. Worms are in the same form all their life where caterpillars are a stage of butterfly or moth.
The reason I spotted the hornworm was because it was covered with delicate cocoons. This was thrilling because these cocoons meant that Braconid wasps were in my garden. These parasitic wasps are only 1/10 to 1/4 inches long and are one of the most important beneficial insects that prey on aphids and caterpillars. It is one of the reasons I plant yarrow in my garden because I know they love the nectar from the flowers.

Braconid Wasp

These predators first insert their eggs in the caterpillar. These eggs hatch and the larvae begin feeding on the caterpillar’s organs causing its death. When the larvae finish, they cut their way out and spin these lovely cocoons where they pupate and turn into a wasp again and cut their way out of the cocoons. You can see their little escape hatches in the picture below. Notice the frass (insect poop) on the end under the horn. These droppings fall on the leaves below and are one of the easier ways to notice if you have hornworms since the caterpillars blend in so well. I often look for the frass and then follow up the plant and find the hornworm.

Tobacco Hornworm with Braconid Cocoons

Of course once you see one of these caterpillars you can probably find a half a dozen or more. As I looked more closely I found three more covered in cocoons and three that had no signs of attack and were eating fast and furiously. I debated for the afternoon if I should leave the ones eating so they would be available for an appetizer for newly hatched wasps but watching my plants get devoured was not easy. I have 6 very robust plants with an abundance of tomatoes and can take a bit of eating but if you only have a small patio tomato these culprits can eat it in one day! I am a big believer in biological control but sometimes it is too slow for my liking.

I decided to remove the three apparently healthy caterpillars but just in case they had wasp larvae in their bellies I placed them out into the forest a good distance from my tomato plants in hopes the wasps can complete their cycle.

This experience reminds me to continue to monitor my garden closely every day and research the critters living there. Search carefully and be sure to check undersides of leaves of your crops. If you see bugs, eggs or frass don’t ignore it. Find out what it is before it does severe damage. This can prevent a lot of discouragement and disappointment in gardening. Some of the insects you find may be beneficial like the cocoons I found. If we’re lucky nature will keep everything in balance with just a little help from us.

Thanks Ann! 

©Copyright 2011 Janet. All rights reserved. Content created by Janet for The Queen of Seaford. words and photos by Janet,The Queen of Seaford.


  1. When I teach my unit about water ecology (6th science) I talk about the effects of pesticides on aquatic wildlife. I always show my students pix of tobacco hornworms and the wasps that use them as larval food. The kids love how gross it is but it really drives the point home. Great post!

  2. I found 2 yesterday, killed them, told my mom who knows a lot about this stuff. Then she told me those ravenous things become the hummingbird sphinx moths which I really love. What to do! She and my dad used to cage and feed the hornworms, having the cage set part way into the dirt so they could pupate there. Then they would leave the cage open later so the moths could escape. I will hate killing them now, knowing who they become.

  3. I get these occasionally but have never really looked closely to see if they were tomato or tobacco. I need to pay more attention. I think I have tobacco hornworms because they are always eating my flowering tobacco. I don't mind it at all. They can have all they want here because the flowering tobacco self seeds quite a bit more than I'd like. I have seen those wasp eggs before. Poor caterpillar I suppose. What an awful way to go.

  4. Thank you, Sande!! Every time I hear about how people hate hornworms I want to scream. I realize they can devour plants and wreak havoc but eventually they become the wonderful sphinx moth--a nighttime pollinator and all around cool garden visitor. Maybe people can do what she suggests. Cage and feed them so they will pupate successfully instead of being so quick to assume they're an enemy.

  5. Evening all, trying to get back to responding to all my commentors.
    Casa Mariposa, What a great teaching tool. I used to take kids through the garden in Virginia and boy, if we found a spittle!

    Sande, It is a delicate balance in the garden. I like your mom's idea of caging them to allow those cool Sphinx moths to come.

    Tina, I hadn't looked closely before. I always thought they were tomato hornworms....learn something new every day!

    Grace, it isn't the hornworm I hate, it is the loss of the tomato that I don't like....especially when I have pared down to one plant on the deck. I do think the caging is an interesting alternative.

  6. Janet,

    Meg finds our hornworms most of the time. I used to find them easily but now they escape me every time. Good read, always enjoy learning new things.

  7. I hate those Hornworms, they almost blend in with the foliage & stems. I pick them off and squish them.

  8. Very interesting and informative.

  9. Quite educational. I've not seen them, but I don't have tomatoes, etc.

  10. They eat our ornamental tobacco as well as the tomatoes. As annoying as the hornworms are, they turn into beautiful Sphinx moths.

  11. Such great photos! I know the hornworms turn into Sphinx moths, and I know if they're covered with the wasp cocoons they'll eventually die, but...I don't want them eating my tomato plants! If I find them in the veggie garden, I destroy them immediately. But it is pretty cool how nature provides such natural predators for annoying insects. I'm still waiting to find something that likes Japanese beetles:)

  12. Great pics. I have found horn worms on my tomatoes but never looked to see which they were. They sure can eat a tomato vine in nothing flat.

  13. They are bad, but oh! they are also beautiful, don't you think so?
    We had a lot of them in Missouri, but not here in WA. Too cold?

  14. Randy, Sometimes I see them right away and others I have to look for a couple days....until they eat more of my tomato plant and get bigger.

    Racquel, they do blend in quite well!

    Darla, I thought so.

    Cameron, I thought it was a good article.

    Sweetbay, I will have to check my ornamental tobacco...didn't even dawn on me.

    Rose, I like the cocoons that are open. I don't like them eating my tomatoes either.

    Lola, they can eat a tomato pretty fast!

    Tatyana, they are quite interesting looking. I am not sure about why they aren't in WA. Maybe it is the difference between east or west of the Rockies.

  15. Thank you for this very useful info, Janet! Though I have to see the pics gross me out! Ha.

  16. This was really interesting! We don't see them here. Really great pictures.

  17. I hardly ever see them here but I wouldn't be able to squish them for sure. How gross to have the wasp larvae eating them from the inside out. It sounds painful to boot especially when the caterpillar is helpless against it.

  18. Fascinating - and beautiful photographs. Love the cocoons - what a grisly but effective way to reproduce.

  19. Very interesting. I love the way you let nature keep things in balance with just a little help.

  20. Ginger, you think these are gross? hmmm, will have to step it up!

    Casa, got it!

    Catherine, I guess you all don't have them out west.

    Kathleen, I let them out for the birds or if they can survive off my tomatoes, they can live!

    Janet, my friend Ann did the photos, she is good!

    NC, it is all a balance isn't it?

  21. thank you for the mention, janet, and all the additional info. those critters are definitely fascinating! incidentally, tobacco hornworms are the ones eating my tomatoes. who would've thought it could be either/or?


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