Tobacco Hornworm

July 11th, 2008 by David LaFerney Leave a reply »
tobacco horn worm

actual size believe it or not

Sooner or later you are going to encounter this little beast – the Tobacco Horn worm (Manduca sexta) munching on your tomatoes or peppers. He has a close relative called the tomato hornworm which for all practical purposes is the same thing, and despite the names they can infest a variety of your garden plants. For example that tobacco worm in the picture is on one of my celebrity tomato plants – you might also sometimes see them on eggplant, and potato plants. They can do a lot of damage in a short time so keep an eye out for missing foliage like this…

tobacco worm damage

… or worm poo like this…

If you see those things then a horn worm is somewhere on that plant rapidly defoliating it. Despite the jumbo size they really blend in well – they take on the color of their diet, but if ye seek ye shall find. Tip: they thrash around when sprayed with water and are easier to see.

Organic Control of the Tobacco HornWorm
The best way to control this little monster is to just stay alert and pick them off and squash ‘em. Despite the large size – commonly up to three inches long – and ferocious looking red tipped stinger thingy, they are completely harmless. Usually hornworms don’t occur in large numbers, and hand picking really is a practical control. If you happen to come across one that looks like this -

parasitized horn worm

Just leave it alone to die in peace, those white things are cocoons of parasitic wasps, which will hatch out and do your work for you if you let them. Yet another reason not to blindly spray insecticide around your garden. Parasitic wasps are common just about everywhere even though they are so small that they mostly go unnoticed. As long as you don’t wipe them out by spraying every thing with pesticides they will naturally be attracted to your yard and garden by many kinds of herbs and weeds with tiny flowers – clover, mint, fennel, Queen Anne’s Lace, Joe Pye Weed, etc. Unless your yard is a chemical soaked golf-green-like monoculture of bluegrass and azaleas you’ll have parasitic wasps around.

If you simply must spray something for life to be complete then Bt – Bacillus thuringiensis – is a completely safe biological control that is effective against all kinds of caterpillars – especially Bacillus Thuringiensis Kurstaki or BTK. When caterpillars eat foliage that has been sprayed with BT their digestive system shuts down and they’re unable to eat and they die within a few days. Compost tea apparently has a similar effect. BT can be found in most serious garden centers under various trade names in both dust and liquid concentrate forms. Our local big box doesn’t have it – I guess they didn’t have room for it once they stuffed the shelves with petrochemical poisons.

If you feel experimental you might try this trick that my Dad used to do – liquefy some of the worms (or Japanese Beatles or whatever the pest du jour is) in a blender along with a cup or so of milk (Yum yum!) and dilute with water, and let it ferment for a few hours before spraying with a garden sprayer. I’ve never actually tried this, but it makes sense that it could work by growing a culture of worm disease pathogens, and basically making them sick with some kind of horn worm Ebola. Or it could just be so disgusting that they move on. I’m sure if someone did that to me it would have one of those effects. In any event during the process you pick off some of the worms and get to play with a kitchen appliance.

Once the caterpillar has eaten it’s fill it will burrow a couple of inches into the ground to metamorphose into the adult phase. Cultivation of the top layer of soil to expose and damage the big brown pupae before they can emerge as moths to lay eggs and restart the cycle is also an effective control reportedly resulting in up to 80% mortality. If you use a no till gardening method (Ruth Stout, “lasagna”, or other deep mulch method) and experience problem levels of hornworm infestation you might consider a preemptive program of spraying BT starting in early summer to hit the larvae while they are still young and relatively weak. Once the caterpillars get big they are much harder to kill, and inflict damage at a much higher rate. I bet that free range chickens would pretty much keep them under control by scratching out the pupae to eat. No wonder free range eggs are so tasty.

Common paper wasps prey on hornworms among other garden pests so think twice before destroying wasp nests near your garden. You might even consider intentionally providing a nest shelter near the garden, but safely located for people.

Carolina Sphinx moth - adult phase of tobacco hornworm

Sphinx Moth Photograph by: John Capinera, University of Florida

In case you were wondering – when they grow up tobacco hornworms become Carolina Sphinx moths, a large brown nocturnal visitor to porch lights all over the south which is actually an important pollinator of night flowering plants. Interestingly enough (if you are a nerd as I am) Sphinx moths, humming birds, and a bat (the name of which escapes me) are the only creatures adapted to hover while sipping nectar. Sphinx moths are sometimes mistaken for nocturnal humming birds. A minor nuisance in the Garden, but beautiful in their way.

The excellent photo of a Shinx moth dining on a moon flower was shot by JohnnyBigFish

This excellent photo of a Sphinx moth dining on a moon flower (a night blooming variety of morning glory) was shot by JohnnyBigFish

The entire hornworm/sphinx moth life cycle can happen as quickly as 30 to 50 days and several cycles may occur in one season given proper conditions. Later in the summer an increasing number of pupae will go dormant in the soil – a phenomenon called diapause. These pupae will overwinter to emerge as adult moths to restart the process next year.

Happy Gardening!

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28 comments

  1. Linda says:

    Stupid code will not enter correctly and it made me lose my text!

  2. jenny says:

    I absoluely hate these garden pests. I wish I did have wasps around. I’m in So Cal, but only bees. I just pick them off my precious tomatos every am and pm Thanks for the tip of the black light, going to check it out this pm.

    • Linda says:

      Jenny, you should realize the moths of this species are quite beneficial. In fact, they do help pollinate your tomatoes. By this time of year, your plants should be large enough to sustain a few larvae to pupation.
      Sure you’re going ot have some stripped stems, but you need to also understand, pruning is also good for the plants, too. If you don’t prune back or let the caterpilars do it for you, you’re going ot have runaway plants, overgrown, more vegetation than fruits.

  3. Linda says:

    I happen to fall into that category of gardeners who don’t mind the nightshade-eating Manduca hornworms. While one can do some damage to a young plant, here in central Oklahoma, nature sends them late enough in the season, to ensure plants are well-established in their growth and foliage. Since hornworms also find the tender suckers as well as leaves, this pruning is beneficial to force more fruit, less leaves.
    Our Manduca hornworms here are largely endangered, and I do NOT recommend or condone the killing of pupae or moths. We have too many tachinid flies [a non-native parasitoid and responsible for wiping out over 33 native giant silk moth species].
    I strongly advise Oklahoma gardeners to give live hornworms to teachers and home schoolers to rear indoors for education. If a larva dies, it needs to be destroyed as it’s full of tachinid maggots.
    By the way, in your picture of the adult M. quinquemaculata moth, the flower is not a morning glory, but a Datura moonflower. The relationship between the Datura and Manduca’s is completely mutualistic, too. This is one valid reason we need our sphinx [hawk] moths!

    • debbie T says:

      Wow, Linda, I love your attitude toward the hornworm. I never thought of it that way, but it makes sense.

      I have only seen a few worms on my tomatoes, and the majority at this point are infected with the wasp larve so I leave those be.

      I do pick off the rest, but they’ve eaten some leaves, and I regularly prune a lot myself.

  4. Alicia says:

    Hi i was wondering if any one knew if there is a plant out there that i can use for my horn worms were it dont make them toxic im tying to breed them for my bearded dragons they say it is very good for them and help gain after giving birth i breed bearded dragons. but i know if they eat the tomato plant it will make them toxic and it will kill my dragons but i tryd fake plants and it didnt work i didnt see no babys or eggs but if any one can help plz do thank you very much

  5. RLeigh says:

    Thanks so much for this info. I have these on my moonflowers every evening and have been searching for their names!
    They are very interesting, as they like to fly into my face as I try to take their picture!!!
    Very neat!

  6. john oddo says:

    I last nigth got a great pic of a Carolina sphinx Moth in my back yard feeding on a moonflower as well it is a great pic i have never seen them before I can only assume they are not indigenous to this area and the hot summer we had may be the reason.

  7. Jennifer says:

    I have one captive for my 5 year old to watch and feed. But, what do I feed it?
    They ate so much of my tomato plant!
    I have basil or mint, but don’t want to give up any more of my poor sad looking tomato plant!

    • David LaFerney says:

      They also eat bell pepper leaves. Good luck with that. You might consider putting an inch or two of dirt in the container so that you can observe it pupating, and emerging as a moth. Very cool Mom!

      • JenniferJennifer says:

        Well, I didn’t have any bell pepper ‘leaves’, but I did cut up a bit of green bell peper from my Mom’s garden and they seem to really like those!
        What about cleaning their environment? They seem to poop an awful lot! ew!
        Oh, and can I put regular dirt or I have miracle grow soil. Which would they like best?

        • David LaFerney says:

          You’re into new territory as far as I’m concerned, but I would think that regular dirt or potting soil that does not have fertilizer added would be fine. Actually it would probably be alright if it does have fertilizer, but you know, on general principles…

  8. powerful says:

    do they get bigger than 5 inch?

  9. Jazmine Johnson says:

    I wanted to know if they r poisonus because i found 2 on my moms peper plant and i took them and put them in my shoe box?And i took them to school,i think that is pretty stupid of me to do that.

    • David LaFerney says:

      Jazmine,

      Not to worry. They are completely harmless. That thing that looks like a stinger is just for looks. They don’t bite, and they don’t sting. All they do is eat your pepper plants. Taking it to school was a great idea. If you feed it leaves from the same kind of plant that you found it on, and put an inch or so of garden dirt in the bottom of the jar or whatever you have it in, it will eat until it is ready to burrow into the soil and then it will become a rather large and pretty moth. Good luck!

      David LaFerney

  10. Helena Van Brande says:

    I found 8 of these caterpillars in my tomato garden, and im keeping them captive right now. But boy, do those eat a lot! (I live in southern California)

  11. Stephen Roberts says:

    I picked one of these up in my garden yesterday and I live in england bristol
    so they are not commmon

  12. Sarah H says:

    Hi I am certain that I have just seen one of these in my Garden, I live in Kent in the SE of England UK. Is it possible?

    • David LaFerney says:

      Anything is possible. Supposedly they are only distributed in North and Central America, but that certainly encompasses a wide enough range of climates to make their survival in Britain feasible. I hope you are mistaken, but they aren’t really a big problem here.

    • ShaunD says:

      If you saw the caterpillar, they look very similar to Poplar Hawk Moth larvae – which are native to the UK (including Kent).
      Not sure whether we have any adult moths looking quite like that though.

  13. tara hedgecock says:

    i have found a 5 inch hornworm on my tomatoe…im kind of scared of it. however, my brother wants to keep it as a “pet”-is there anyway to raise these little fatties like you would a butterfly in school, or would it die in a cage?

    • David LaFerney says:

      I don’t really know, but I don’t see why not. Feed it until it pupates and give it a little bit of dirt to burrow into and find out. Let me know what happens.

    • Ramey says:

      Hi! You can indeed keep them in captivity. Just make sure you give them plenty of food, and when you see their dorsal vein or “heart” start pulsating and the larva stops eating, shrinks in size, that you give it a few inches of soil to pupate in. In 3 weeks, you should have a moth! I have one right now in pupal stage. Good luck!

  14. @John Feaster – I’ve only seen one of them myself, and it was big enough that at first I thought it was some kind of rare nocturnal humming bird. It was feeding on some honey suckle flowers just after dark in early summer (in central Tennessee) I guess spotting one of the adults is unusual enough to qualify as a treat.

  15. John Feaster says:

    How big do these dang things get, because I’ve seen two of them in my life (I live in northern Indiana), and one of them had a body the size and thickness of my index finger. I remember seeing it outside the window – fluttering against it for more than three minutes – and I said “You could cut steaks from a moth that big!”!

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