Last updated on July 23rd, 2013
RECENTLY, while pruning a row of paste tomatoes, I noticed a strange-looking worm (above; click to enlarge) on one of the plants. What this worm is, why it has white projections on its body, and why — if you ever see such a thing in your own garden — you should leave it alone:
A quick Google search revealed the odd fellow is the Tomato Hornworm. This Manduca quinquemaculata feeds on the leaves and stems of tomato plants, as well as other plants in the Nightshade family, like eggplant and potatoes. It can devour an entire plant in a matter of days. Worms should be picked from plants, and dealt with as your conscience permits.
However, if the worm has white ovals on its body, you should take no action at all. The white projections are the larvae of the braconid wasp, Cotesia congregatus. Larvae that hatch from the wasp’s eggs, which are laid on the hornworm, feed on the inside of the hornworm until the wasp is ready to pupate. Such “host” hornworms should be left in the garden in order to conserve the beneficial parasites. The wasps will kill the hornworms when they emerge from their cocoons. They will also seek out other hornworms to feed upon and kill.
Want to attract this hornworm-destroying wasp to your garden? Then plant, and preferably near your tomatoes, such things as parsley, dill, yarrow, and mustard. Adult wasps feed on the nectar of these plants. Also, provide a source of water. A birdbath will suffice.
And finally, I hope you won’t scream if you notice a host-hornworm on your tomato vines. For it means your garden is ecologically balanced, thanks to your non-use of pesticides.
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Lisa F says
Wow, good to know! We have been freaking out with the hornworms on the tomatoes. Thanks!
Kevin Lee Jacobs says
Lisa F – Hornworms are strangely-beautiful. But they are also very destructive. Maybe try to encourage the braconid wasp to visit your garden?
The Japanese Redneck says
Very interesting. I'm going to have to see if hornworms are what my hubby calls a tobacco worm.
Kevin Lee Jacobs says
The Japanese Redneck – Tomato and tobacco hornworms are very similar. Both are preyed upon by the braconid wasp.
Anonymous says
What happens when the wasps hatch? Are they the same stinging wasps?
Kevin Lee Jacobs says
Anonymous – Yes, they are the same wasps which will go on to kill other tomato hornworms. The wasps, by the way, are not known to attack humans.
Broken Barn Industries says
Very cool post. No hornworms here but I'm glad I know now to watch for the larvae. It makes me cringe to think how many times in the past we SPRAYED the wasps nesting behind our shutters. We were ignorant about their benefits 🙁
Kevin Lee Jacobs says
BBI – Not all wasps are the parastic braconid-type. The braconids are tiny, and — I've just discovered from further research — they are harmless to humans and pets. So probably not what you have behind your shutters (I have the nasty stinging-types behind shutters here, too).
Anonymous says
Thanks Kevin! I found 4 in my 2 cherry tomato plants! I've never seen one before, all 4 have the parasites though 🙂
Marilyn Wilkie says
Hi Kevin,
We have picked maybe 16 Tobacco hornworms off of our 6 tomato plants. I know they are tobacco hornworms because their stinger is red. None have the wasp larva unfortunately. They are hard to spot..blend right in. Look for their scat which are little black ball s. They eventually turn into beautiful sphinx moths. I've seen a few this year around my garden along with hummingbird moths and bumblebee moths. The worms remind me of Alice in Wonderland…tobacco..hookah??? LOL
Yaxue says
Thanks Kevin for this edifying tip! I haven't been taking close look at my tomato plants, and now I know what not to do with it if I see one. And it's comforting to know it's actually a sign of goodness….smile.
Kevin Lee Jacobs says
Anonymous – Four out of four had the parasites? You are blessed indeed!
Marilyn Wilkie – LOL – yes, the hookah-smoking caterpillar!
Hornworms — tobacco or otherwise — are really hard to spot. I only noticed mine because of the white cocoons the wasps had spun.
Yaxue – As you said, definitely a sign of goodness!
Tammy says
Kevin, I reached in to pick some tomatoes this afternoon and came nose to nose with a hornworm. Then I saw several more near it. Most, but not all, had the white larvae, so I'll leave those be. But what of the ones going about their merry munching way? I'm trying to figure out if they too will be visited by the parasitic wasp soon or whether waiting could give them too much time to wreak damage. Any rule of thumb you use to decide how long to give the healthy suckers a chance to become larva hosts? Thanks!
Kevin Lee Jacobs says
Tammy – When one parasitized hornworm is present, I leave the others alone. The young wasps hatch quickly, and SHOULD immediately attack the other worms.
Tammy says
Thanks, Kevin, that sounds like a good plan.
Anonymous says
How long does it take the wasp to hatch?
chickory says
I am so glad I found this and read it – i’ve seen this in my garden every year and yet i am so woefully ignorant of garden pests I fed these worms to my chickens not knowing I was killing a garden helpmate. But i was stoked to read my garden is sound because they are present. I look forward to seeing it this year. thank you!
Kevin Lee Jacobs says
chickory – Nice to meet you. I was stoked, too, to discover I had beneficial insects here. They work in strange ways, huh? Hope to see you again.
Eica says
I hope I see some, as last year we had a bunch of hornworms! Is that bloodthirsty, or what!? Haha, still, I hope to see those white ovals sometime soon. I always have dill, and other herbs around the garden. I wonder what keeps the wasps away? Are there any plantings that discourage them (so I won’t plant that IN the garden)?
Kevin Lee Jacobs says
Eica – Nice to meet you. Bloodthirsty, yes, but in the very best way! Only the presence of pesticides will keep the beneficial braconid wasp away.
Tina says
Hi there,
I had hookworms several years ago. I researched the Worm. ( It was a great learning experience for my daycare children) I read that if you plant baseil near your tomatoes it will keep the hookworms away. I have been planting basil near my tomatoes for the past 3 years. I have not seen a hookworm since!
Lisa says
Had big infestation of hornworms last summer. Tried to pick them off & give them to the chickens, they weren’t interested. Then I picked of a branch that had the worm on it. Dangled branch with worm in front of the chicken & she snatched it right up. After the other 2 got sight of the other chicken eating a nice juicy worm they all 3 would go through the tomato patch snatching the horn worms right off the plants. No more horn worms!! (no the chickens did not start laying green eggs 😛
Pat Knoyyd says
How can I get rid of squash bugs?
CATT says
The only thing is, by the time the wasp larva hatch the tomato plants may have been destroyed. Actually, I have never seen the larva of wasps on any horned catepillars, but I had these these dratted things attack my 8 heirloom tomato plants, growing in pots in my courtyard. It was pitiful, because I now had the plants protected from the critters (rabbits. gophers, squirrels)(we live in the rurals) and then to have them destroyed by, these critters, was heartbreaking. I’m now planning an enclosed greenhouse and going with either hydroponics or aquaponics.
Grace says
“Larvae that hatch from the wasp’s eggs, which are laid on the hornworm, feed on the inside of the hornworm until the wasp is ready to pupate.”
The eggs are actually laid *under the skin* of the hornworm, not *on* the hornworm. The female wasp uses her ovipositor (the tube through which eggs are laid) to deposit the eggs just under the hornworm’s skin.
The white things you see on the hornworms’ backs are not eggs: they the cocoons of larvae that have fed on the hornworm’s innards, then emerged through the skin when they are ready to pupate. When the “lid” of the cocoons have been popped open, you know that the wasps have emerged. By the time you see the white cocoons, the hornworm can no longer do any more major damage. It is very close to dying.
Reba says
I think here in Texas we call them “cut worms.” I had them a lot this summer. I put in organic beds last year and they seemed to moved in this year. I hated killing them. Now I know what to do with them. Thanks.
Tara Woodruff says
Excellent Article!! Thank you Much!!
Diana DeJane says
very cool article, although I already knew this as I saw some of what you described and googled it. I find hornworms fascinating in a weird way, they creep me out but they remind me of little aliens, like the one that came out of that guys stomach on Alien..kind of cool looking! They are hard to spot on the green leaves for sure but I leave the larvae worms alone but pick the others off, they can really do damage but you have to really search for them. Actually I used to have chickens but they were as destructive as the worms cause they LOVED to eat the tomatoes! Darn chickens! LOL
Tracey Santi says
I am new to veggie gardening and happened upon an unfortunate sight in my garden this morning. Relieved to have made it through this horrible heat wave to go outside and find that something has eaten a lot of my sun gold tomatoes and the tops of the plant! Google to the rescue and I stumbled across your article here. I found it so interesting that I went outside and sure enough…found one of those stinking hornworms chilling on my plant. Sweet justice though, it is COVERED in braconid wasp pupae. I felt such a sense of victory. I battled and picked beetles off of my plants and wet the whiteflies and I had not seen any “cavalry” til today. I love what you said about having a good balance. I bought insecticidal spray but couldn’t bring myself to use it. This morning, an assasin bug waiting on my basil for leaf hoppers. Ladybugs on my peppers and eggplants with no sign of the few aphids that were out there. And now these hornworms are being attacked. Thanks so much for your article. I would have tossed the HW in the road thinking it was carrying around its own eggs. It really is all about balance.
sb says
What about keeping them in a jar untill the larva hatch????
Sharon Shade says
My first attempt at a real garden since I’ve moved to TN and while I never saw any worms on my tomatoes, I did see the above fellow on my red pepper plant complete with the white larvae. My garden had nothing but dirt and compost. So everything was totally organic. Happy it left my Roma tomatoes alone because they were amazing.
Roxanne Gordon says
I noticed my tomato plant loosing leaves about 2 yrs ago. I looked very close for bugs and was grossed out when I saw a leaf….move….it was a huge fat caterpillar. I read on line they hate water. If you can’t find any on your plants, spray the plant with water and they will start to curl up.
I got a water bottle, sprayed the pants and ….bingo…there they were. The plant was too far gone to save, and I’ve never bought another plant again.
Yesterday I saw at the garden center tomato plants about 2′ tall, thick stems, small tomatoes, with a sturdy support and thought if I put that on my deck would it be safe from the dreaded worm?? After reading these comments the answer is NO. I would have to pick ‘e off, or push them into a can of soapy water till they drowned and/or use chemicals.
Now I’m wondering about a net? A lightweight net that is used to keep deer away from flowers, if that would work.
wow….a full time job growing tomatoes. Not sure I’m up for that. I have a family issue out of state so have to drive 2.5 hr each way every weekend. I’ll have to buy my tomatoes across the street from the local farmer. I’m sure he’ll appreciate the business.
Joe says
Any advice on killing the braconid wasps themselves?
Tara says
So before learning what tomato hornworms or braconid wasps were I hand- picked like 12 of them off my tomato plants. All had the parasites present. I threw them in a nearby field “alive”, but should I have just left them? And have I damaged my chances of future protection from the hornworms? I planted lots of dill, basil & parsley nearby. So they must be doing their job! 😀
Nadege says
If you have bearded dragons they love eating horn worms.
Nadege says
You shouldn’t kill them they are a beneficial parasite.
Kass Freese says
Well, snap. I already killed it before I knew what was up. I found a big ol’ hornworm which I dispatched immediately. Then saw the affected one, and removed it before seeing this article. But I will remember in the future to let those be.
kathy says
i have grown tomatoes successfully for over 20 years. for the first time this year something was eating the nicest ripest tomatoes right on the vine. Someone said it was rats! To my horror I put some mint plants around the base of the tomatoes plants. i started picking the tomatoes a little earlier and put the in the house on a table to ripen the last little bit.i went away for the weekend and on my return all of the tomatoes had been eaten. do not know how something knew the tomatoes were in the house or how it got into my house. Not a fan or rodents, any ideas what is going on?
Robin says
I usually throw any hornworms I find to my chickens, but I’ll be on the lookout for worms with wasp eggs and leave them alone!
Nancy J says
Do tomato hornworms also devastate dill? I saw some worms on the dill that looked just like the tomato worms but smaller and they had stripped the dill.
CJ says
If I see any I will cut those white things OFF of my tomato hornworms!!
Laney says
Nancy J — Hornworms don’t eat dill but the caterpillar that ate your dill is probably the Eastern Black Swallowtail. They are beautiful butterflies, I actually raise them indoors because my kids love to release the butterflies. I don’t mind sacrificing the dill for them, and actually planted rue which became a big bush that they like to eat too.
Now hornworms, on the other hand, get instant death. And today I finally saw one that had been parasitized. Yay!
Laine Leavitt says
Am I the only one who is sad when I find an infected hornworm? These massive caterpillars turn into a large, beautiful sphinx moth…..a pollinating benefit in their own right. I grow a separate plant a short distance away from the others and when I see a hornworm, I put him (her?) On it. This is my sacrificial plant. I can not in good conscience kill a future pollinator. For the folks out there using insecticidal soaps and insecticides. …really? It kills the good bugs, too. Let nature be….
Sodbuster says
I’ve never seen one infested with wasps here in northeast Ohio. My kids would catch them, put in a jar and feed tomato plant parts. They make an interesting summer pet for a little while.
Shannon Touw says
We brought an infected horn worm inside and put it in a jar with part of the tomato plant. Should we return in to the garden? I don’t really want wasps flying around or emerging in my jar. How long does it take for the pupae to emerge once you see the white cocoons on the worm?
Yvetta Williams says
They turn into humming bird moths and are our night pollinators. They are very good for the gardens. Plant an extra tomato plant and move them onto that leave the others to become hummingbird moths. WE NEED THEM!!!
Yvetta Williams says
They turn into humming bird moths and are our night pollinators. They are very good for the gardens. Plant an extra tomato plant and move them onto that leave the others to become hummingbird moths. WE NEED THEM!!!
Heather says
Ok so we found said tomatoe hornworm today sho had eaten the top part of the plant. At first my hubby googled and it said to drop them . We put it in a bucket for about 5 minutes Nd I couldn’t watch it suffer anymore and threw it in the back field.. they are huge. Should I just leave it next time? Couldn’t do d My others but one or two tomatoes were eaten as well like half gone.
Heather says
Ok so we found said tomatoe hornworm today sho had eaten the top part of the plant. At first my hubby googled and it said to drop them . We put it in a bucket for about 5 minutes Nd I couldn’t watch it suffer anymore and threw it in the back field.. they are huge. Should I just leave it next time? Couldn’t do d My others but one or two tomatoes were eaten as well like half gone. .hmmm
Pati says
I leave the tomato hornworms alone for the most part. I plant enough for all of us. The moths are becoming endangered and they are beautiful. Live and let live as much as possible (I draw the line at mosquitos, yellow jackets, mice and rats invading homes, etc.) and try prevention as much as possible.
Ruthanne says
@laineleavitt Finally a kindred soul. I found one today and thought they were eggs. I goggled, and you know the rest. When I read the parasites were eating the hornworm from the inside out, I became strangely sad. My first instinct was to go out and pick them off. Then I read that the hornworm was already dying. I still can’t feel the jubilation that’s others have. Ridiculous, I know.
Jonh Sweetman says
What else can I feed hornworms as I have a couple in a terrarium for my granddaughter to watch?
jessica says
i love my plants SO much and work hard to keep them happy, but i can’t understand how most of you guys are so joyous about a living creature being eaten from the inside out!! i mean, aren’t you nature lovers?? it really upsets me to think how painful this must be for the hornworm.
never mind the fact that it’s super exciting to see a beautiful hummingbird moth show up every now and then and help pollinate my garden!
Jennifer Drysdale says
Just a very friendly reminder that these turn into very important nighttime pollinators. I welcome them into my yard every year and grow extra tomato plants just for them.
Jeannie Jenny says
Yeah I agree about killing things just because we don’t like them. I will plant a tomato plant or 2 farther away and transfer them when I find them
Garden Life says
I’ve planted tomatoes many times over the years and I have seen hornworms on my plants but I’ve never seen the wasps on them. Today was the first time. And I have to say I do feel bad for the horn worm but it’s all nature doing it’s thing. And this guy is too far gone at this point. :/
Garden_Life says
On the other hand, via http://www.Internationalbutterflybreeders.org
“ Tachinid flies and braconid wasps are two parasitoids that feed on and kill monarchs. These parasitoids lay their eggs on the caterpillars. Tachinid fly larvae feed on monarch caterpillars, but usually don’t kill their hosts until just before the caterpillars pupate.”
Maybe I’ll put horn worm out of his misery
Estelle says
Well I screamed and almost cried when I realized what was under the white eggs! I wish I’d Googled before turning hysterical. Thanks so much for the post.
Marlene says
I’m so sad. I just went out captured my horn worms and brushed off every white thing I saw. Cut a tomato and some leaves into them. Now I’ve read these wasp eggs are inside this beautiful worm. So does that mean my work was in vein I cannot stand the thought of anything being eaten alive♀️
DJ says
I love parasitic wasps, especially blue mud daubers. I am cool with the braconid wasps doing what they evolved to do in their ecosystem. Whether it is hornworms or even monarch caterpillars (they don’t use monarchs as hosts as much as tachinids), I don’t think gardeners should intervene much, unless this is how you make your living or you depend on the garden solely for your food. We should get on top of issues that we caused though, which significantly diminish all species populations. It’s the domino effect – you lose one species, you lose hundreds, maybe thousands more that are connected.
Jane says
Very ,very helpful!
Thank you Kevin!
+=❤
Judith says
I have always been taught that wasp lay their eggs on the tomato worm, when they hatch they feast on the worm until they ready to be on their own and the dies. Must be a painful death.
Judith says
The worm dies. Couldn’t find a edit in the site