Search

Search My Garden Blog with Google Custom Search

9.9.13

Tomato Hornworms and Parasitic Wasps

After squirrels and deer, the tomato hornworm may be the bane of a tomato grower's existence. Fortunately, tomato hornworms and parasitic wasps go together like tomatoes and basil. Finding a tomato hornworm in your garden is not the end of the world if you catch them early, and if you employ natural gardening techniques, they garden is brought into balance by bracondid wasps.

Tomato hornworm in urban garden



Here's a tomato hornworm in my urban garden happily munching away on the foliage of one of my tomato plants. This caterpillar get's its name from the vicious-looking horn at one end of the body. In this photo of the hornworm, you can see the horn on  right side. This caterpillar, should it be allowed to live, pupates into the five-spotted hawkmoth--a brown and gray hawk moth--in the Sphingidae family.

Tomato Hornworm poop

Identifying Tomato Hornworms


It took years of gardening before I ever spotted a tomato hornworm in my garden. And when I finally did see them growing on my tomato plants I wasn't upset. On the contrary, I was rather excited to see this garden pest in my garden. I like bugs, and bugs happen when you garden. If you're hunting hornworms on your plants the first sign you may see is the caterpillar's poop. For a rather small bug the hornworm leaves behind some rather large poop trails. They look a little like mouse droppings and you'll see them on the leaves of your tomato plants, or if you grow tomatoes in containers, you'll see a lot of them on the ground around your pots. Tomato hornworm poop is really hard to miss.

Parasitized tomato hornworm

A parasitized tomato hornworm in my garden this year. Notice the the tomato hornworm is covered with cocoons of pupating braconid wasps. The braconid wasp is a parasitoid of the hornworm because it kills the hornworm as it pupates. If you look closely, you'll see a drop of something emerging from the left side of the caterpillar and from among the cocoons. I'm not sure if the secretion is something the caterpillar does normally, or if it's occurring because of the wasp eggs. But this year I noticed a high presence of wasps on my tomato plants and after observing them, they seemed to be drawn to the sticky secretion. So a high number of wasps and bees on your tomato plants is another sign to look for when identifying and locating tomato hornworms on your tomatoes.

Eliminate and Control Tomato Hornworms 


tomato hornworm prasitized

Don't go with your instinct and reach for any bug sprays or synthetic chemicals if you spot tomato hornworm damage on your plants. You are, after all, going eat those tomatoes at some point. Instead, pluck off the hornworm by hand and dump them into a bucket, pail or glass of soapy water. Alternately, you cut them into pieces and feed them to birds that visit your garden, or see if your backyard chickens would like a fat, juicy treat. Some chicken growers I've talked to said their hens turn their nose up at the hornworm, but the chickens and roosters that live in the parking lot of the laundromat I use seem to love them.

Hornworm tomato pest

My absolute favorite method of controlling hornworms on my tomato plants is to save a few of these caterpillars and let nature take its course. Pull the hornworm from your plants and place it inside a jar or plastic bottle without a lid to allow for ventilation. Every couple of days add a few tomato cuttings to the container to allow the caterpillar to continue to eat. And then sit back and watch as the hornworm is eaten from the inside by the pupating parasitic wasps. It's so disgusting, but it's so much fun to watch. This has the added benefit of ensuring that there will be parasitic wasps around your garden the next season to help you eliminate and control tomato hornworms on your plants.

How do you handle the tomato hornworms in your garden? Do you pluck them, or do you leave them for the parasitic wasps to devour?




49 comments:

  1. I don't have a ton of tomato plants, so I pluck them.

    So far I haven't come across one that's been parasitized, if I find one I may keep it just to see how it develops!

    ReplyDelete
    Replies
    1. Hi Mysterious Gardener,

      When I first started finding them in my garden, I didn't notice any of them being parasitized. But then I left them on the plant for a day longer and noticed that they were full of the cocoons a day later. It may be that the wasps just haven't found them.

      Delete
    2. You won't notice that they have been parasitized until the final stage of the process -- that being the appearance of the wasp cocoons on the caterpillar's body. The process begins long before the cocoons appear. The wasp injects her eggs into the caterpillar. The larvae hatch and feed on the caterpillar's body. Occasionally, particularly if the caterpillar is back-lit,you might see worm-like bodies moving inside it. Once the wasp larvae have finished growing, they emerge from the caterpillar's body and create their cocoons in which they pupate. The wasps eventually emerge to start the whole process over again with a new caterpillar.

      The original caterpillar may continue eating for a short time after the wasp larvae have cocooned, but it will never survive long enough to pupate itself -- the internal damage caused by the wasp larvae is simply too extensive.

      Delete
    3. Forgot to add, both for pollination purposes as well as to attract the paracitoid wasps, include small flowered plants like alyssum which bloom early and heavily. Both our native diminutive solitary wild bees as well as the paracitoid wasps (which are also very small) prefer flowers that are small or composite flowers (like those of black-eyed susans and such) from which to feed.

      Delete
    4. Paul, Thanks for adding such interesting, information to how the wasps parasitize the caterpillar. I really appreciate it!

      Delete
  2. We have never had them, maybe because we are growing on the roof. Your description at the end was intense!

    ReplyDelete
    Replies
    1. Hi Brooklyn Farm Girl,

      Maybe being a rooftop gardener has some advantages. It took almost 8 years of gardening outdoors to finally have the moth find my tomato plants and lay some eggs. Capturing them and feeding them to keep them alive so that the wasps find them is really gross, but a little exhilarating when you see the caterpillar start to be eaten from the inside out.

      Delete
  3. We had them this year for the first time. Using my snippers, I cut them off just below the stem they were sitting on. Then I stuck them in a zip bag. After sliding it closed, I sat it in the sun and let it fry.

    ReplyDelete
    Replies
    1. Modern Mia,

      I like your method. It's cruel and unusual, lol. I feel like sticking some on bamboo skewers and placing them around the garden as a warning to other tomato hornworms that may be around. ;0)

      Delete
  4. I even didn't know they existed !

    ReplyDelete
    Replies
    1. You know, it took a number of years of me growing tomatoes in my garden before I ever got a single hornworm. I don't know what took them so long, but now I wonder what other kinds of garden pests have yet to make an appearance in my garden.

      Delete
  5. I have never had a major problem with hornworms and let them be. Don't pluck 'em or kill 'em, they get to stay. Someday if I'm ever infested I might change my tune, but not for now.

    ReplyDelete
    Replies
    1. I have that same live and let live philosophy with a lot of garden pests in my garden. They don't get hunted down unless they're doing something really bad. In this case, they are messing with a tomato I use to grow a seed bank so every plant and fruit counts. :0)

      Delete
  6. I have had them off and on, usually left them because they looked so frightening to me! I have always had enough tomatoes whether or not I have had them on a plant.

    Eileen

    ReplyDelete
    Replies
    1. Eileen, LOL. I know what you mean about hornworms looking frightening. I've been sitting in the porch garden many a time and have caught one inching along a tomato plant out of the corner of my eye and needed a change of shorts. They're so disgusting-looking.

      Delete
  7. I had them in Colorado, but I just left them and let them do my pruning for me. I ended up with plenty of tomatoes. Also, the hummingbird/sphinx moths they become are among my favorite creatures.

    ReplyDelete
    Replies
    1. Botias, Yeah, killing off that pretty moth is the only thing that give me pause when letting the hornworms get eaten up. I'm glad someone else can appreciate them too.

      Delete
  8. What a grim post! But bugs eating my plants make me sad too. Wasps are our bros after all.

    ReplyDelete
    Replies
    1. Sandy, Gardening is a grim business. Wasps are only our friends when they're killing off pests. Otherwise they're mean bee-impersonating, territorial bullies in my garden. :0)

      Delete
  9. I don't have a ton of tomato plants, so I pluck them and toss them into the trash bin that holds garden waste. I hope that they continue to feed and meet their maker in due time, but away from my plants.

    ReplyDelete
    Replies
    1. Enzie,

      I bet they wasps find them in there too. So it sounds like a great way to deal with hornworms in my book.

      Delete
  10. Ellen from Georgia9:59 AM

    If I find them I feed them to my hens, they fight over this big green tomato horn worm. This year my raised beds didn't have any but down in the main garden well it was full as usual.That would be lots of afternoon treats for the hens. Ellen from Georgia

    ReplyDelete
    Replies
    1. Ellen, Thanks for chiming in here and sharing your experience with feeding hornworms to your hens!

      Delete
  11. What the big-footed bugs didn't devour of my tomato plants, the hornworms finished. But I don't mind too much. Now I'm enjoying the moths. So cool! Love that pic of the desiccated hornworm.

    ReplyDelete
    Replies
    1. Walk2Write, Are you still in Florida? I shudder at the size of the some of the garden bugs I've seen online in your neck of the woods. But yeah, the moths are pretty aren't they? The first time I saw one in my garden I thought they were hummingbirds.

      Delete
  12. Wow! Very cool pictures! And ofcourse the information is invaluable..

    ReplyDelete
    Replies
    1. Thanks Love, Live and Garden!

      Delete
  13. Planting borage near my tomatoes has worked wonders. Not a single hornworm in two years. The borage self-sows and volunteers can be transplanted if you're rotating crops. Pollinators love the borage and you can avoid hornworm execution altogether.

    ReplyDelete
    Replies
    1. Tony, Thanks for the tip on planting borage with your tomatoes to keep the hornworms at bay. I hadn't ever thought about that, but I'll give it a try next year.

      Delete
  14. Tony's right-companion planting really keeps the bugs where they belong: elsewhere! Borage is so pretty, too.

    ReplyDelete
    Replies
    1. Thanks for backing up what Tony suggested. I'll give it a try next year and see if it works for me too.

      Delete
  15. I really was amazed by your images and your patience raising the hornworm until its demise. Like watching a TV nature show...

    ReplyDelete
    Replies
    1. Garden Walk, LOL. Well, these are the lengths I'll go to for a semi-fun and informative blog post :0)

      Delete
  16. i've had run ins with hornworms before, but never with these parasitic wasps, and boy do they look weird, i think i'll freak out if i see them doing that to the hornworm, perhaps it's the weather here that doesn't allow the wasps to thrive, but it's good to have been warned, i won't have to freak out when i finally meet them

    ReplyDelete
    Replies
    1. Maurice, Don't be afraid of parasitic wasps, they're your friends in the garden.

      Delete
  17. Gardening is definitely not for the squeamish!

    ReplyDelete
    Replies
    1. Lily, I totally agree with you.

      Delete
  18. The moths themselves are rather attractive and, as others have stated, are REALLY neat to watch them feed. Members of this family are referred to as "hummingbird" moths because they hover while feeding -- just like a hummingbird. (For that matter, they are about the same size a as a hummingbird.) As adults, they serve as pollinators so they do have their "good" side as well.

    If you happen to be growing a number of tomato plants, let a few plants be set aside for the wild life.

    ReplyDelete
    Replies
    1. Paul, yeah, the moths are really cool. I've only seen the adults in my garden once, but I can appreciate them. Unfortunately, I only grow a small amount of tomatoes for a seed bank that I founded so I need to harvest every fruit I can. Otherwise I'd let them stay around and get pictures of the moths for a blog post.

      Delete
  19. So bizarre looking with the cocoons on them and the whole process of the wasp larvae feeding on the poor caaterpillar is so morbid. Looks like the wasps are your allies here.

    ReplyDelete
    Replies
    1. Stiletto, It is rather creepy isn't it? I wonder how many boys we could turn into gardeners if we exposed them to the creepy and crawling things in the garden instead of trying to make them appreciate flowers? I know if I was a kid I'd be all about the bug wars that happen in such tiny spaces.

      Delete
  20. We may not like Tomato Hornworms, but these parasitic wasps are unfortunately causing much more damage than we think. They are devastatingly invasive, rendering pupae of 90% of all related Hawk Moth relatives - Luna moths, Polyphemus, and most other Hawk Moth species in North America. many native orchid species are becoming endangered due to the decline of Hawk Moth species, particularly the long-Tounged hawk moth. Last year I collected 300 pupae in the winter, and only 2 had viable larvae in it. Hey, I love my tomatoes, and even though this particular species only pollinates solanum, I can't help but be concerned about the realities of overpopulation and more parasitic wasps and fewer sphinx moths. I also love my Ichneumon wasps, but keeping the natural balance is essential if we ever want to experience the annual June emergence of the more magnificent larger moths. I just want to remind people who live in cities and garden, that sometimes, things are not always as they seem, and that even a city garden is part of nature, and the natural cycle of life. Perhaps introducing our non-native solanum species is the problem?

    ReplyDelete
    Replies
    1. Hi Matt, That's an interesting and thought-provoking perspective that you've shared. I wish I had spotted the comment earlier. I hope others who come across this posting scroll down and read what you have to say. Thanks for sharing.

      Delete
    2. Sqweeq5:37 PM

      Super information! People need to know these things before condemning a life! Be it ugly or beautiful! Eye of the beholder I guess! Anyway, thanks for the comment. I know where I stand and always have! Let live what can! We forget sometimes, the gifts of life!

      Delete
  21. Most people that I know who have both gardens and chickens feed their hornworms to their chickens. I usually just let me kids play with them. They usually forget to feed them and take care of them - so the hornworms end up dieing from neglect. If there are too many hornworms then I throw them against a block wall that is right next to my winter garden. They make a very nice soil ammendment. (=

    ReplyDelete
  22. I like your approach to seeing bugs. They happen so might as well accept them rather than freak out. It's a lot easier to deal with them that way when coming from a point of acceptance.

    ReplyDelete
  23. Anonymous7:51 AM

    I have read that there are not many hornworms left but never seen they are endangered though, good! I just think raising them on only the leaves of your plants, if it doesnt kill your plant is good because they are good pollenators and we need pollenators since honey bees are dying out more. Makes great science projects and looks beautiful. Id rather fight with a moth than a bee ANY day. Im trying to raise one but it has wasps. Wiped off but dont know if it will live. Me and my son will be so sad if it dies.
    Ashley

    ReplyDelete
    Replies
    1. Sqweeq5:23 PM

      I too, tried saving and bringing to moth-hood! The one I found looked really healthy, but, as you said; it already had cocoons from wasps( only like 20). I thought I will save this little one! You could see where he was injected, and i thought he might beat the little damage! Wiped off! Than set up a spot outside protected from danger with its own little tomato plant! The next day he was slow! AND, 2 little larvae were emerging from his skin! As I watched one completed emerging! Fluid kept flowing from the exit wound, like 1 hour! He just curled up in agony and fear i bet! Then an hour later the next! It was horrible! I took a hammer and smashed his head and shoulders to nothing in 4 fast blows 2 seconds flat! Then I struggled with my self the horror I had just accounted for! I killed it! But did he, or would he suffer without my interference? I did an autopsy! "I MUST BE NUTS, I KNOW!" But I had to know! Glad I did this guy was doomed from before I got to him! Poor thing had larvae everywhere that a pocket of fluid existed, outside looked fine, insides surrounded! If anyone reading this has a heart or a soul, take these poor victims out of their misery, they would beg you to if they could! Horrible life inheritance-sentence! Horrible! If there is a hell, they live it!

      Delete
    2. Sqweeq5:29 PM

      If I knew how to post a pic! You could see the autopsy results! Trying to not be gruesome! Just insight for other with interest!

      Delete

Hi!

Feel free to leave a comment. You can always use the search box for my blog or the search "Google For Gardeners" if you're looking for gardening information. If you're looking for seed saving information check out "Seed Snatcher"search engine.

Do not have a blog yourself? Comment using the "anonymous" feature. If you have a Twitter or FB account feel free to use the "Name URL" feature so other people can find you.


Thanks for visiting.