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Discrepancies in IDs – Hornworms – Eggs or Cocoons

Tomato or Tobacco Hornworm – Eggs or Cocoons of Braconid Wasp

The biggest of caterpillars – at least in my gardens – are the hornworms.  Fully grown they’re enough to gross-out any gardener, even the most seasoned among us. The ones in my garden are Tobacco Hornworms, although – until the past few weeks — I thought they were Tomato Hornworms.

They look pretty much alike, but there is a difference.

Color of the “horn’

Each has a “horn” at the end of the last segment of their body.  The horn of the Tomato Hornworm is black; the one of the Tobacco Hornworm is red.

White Marks on the Side

There’s another difference. The Tobacco Hornworm has 7 diagonal white stripes on the side.  Pictures of the Tomato Hornworm show 8 “v” shaped stripes.

Large Moth

Another thing I never knew until recently: The adult moth of the Tobacco Hornworm is the large Sphinx moth.  The adult for the Tomato Hornworm is called the Five-spotted Hawk Moth.

I did a google search for pictures of these extraordinary moths and found a lot of discrepancy.  Some of the same pictures came up in each specific search. So amateur moth-identifiers, like myself, may never know for sure which is which.

Host Plants

I grew moonflowers (datura) some years back and remember seeing a very large moth on the trumpet shaped flowers one evening at dusk.  My guess is it was the Sphinx moth since these plants are host to this creature as are tomatoes, peppers, eggplants and other nightshades.

Enter the Braconid Wasp

Hornworms are few and far between in my garden.  Ever hear of the Braconid wasp? (And no – it doesn’t sting.) She and her relatives have been taking care of my hornworms for more than 30 years.

I remember the first time I ever saw the result of her work.  I was a fairly new gardener and didn’t know what in the world it was. I thought some horrible insect was going to take over my garden.

Hornworm with cocoons of Braconid Wasp. Note the red horn and the barely visible white stripes on the side.

 

We didn’t have the internet back then. I don’t remember where, but I must have read something about it being eggs of a beneficial insect. So in ignorance for over 30 years I referred to the white silken cocoons on the back of the parasitized hornworm as eggs of the Braconid wasp.

Evidently, I was not alone. If you do a search for “pictures of eggs on Tomato Hornworm” and then for “pictures of cocoons on Tomato Hornworm” you will see almost identical pictures.

With  a little more information about the Braconid wasp, it becomes obvious they’re not eggs.

For example: When you find out that the Braconid wasp is only 1/10 to 1/4 inch long and lays the eggs “inside” the caterpillar — you realize immediately that the little white things that look like rice are too large to be the eggs of this little wasp.

Furthermore, I learned that the larvae eats its way out of the caterpillar and spins the cocoon from which an adult Braconid wasp will hatch.  It doesn’t have to spin the cocoon on the hornworm, but that’s usually where you and I see them.

So if you see one of these hornworms with white silk cocoons that look like grains of white rice standing up on its back — leave them in your garden so that the next generation of the friendly little Braconid Wasp can help you.  They’ll rid your garden of Tobacco or Tomato Hornworms so you won’t have to.

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All content including photos is copyright by TendingMyGarden.com.  All Rights Reserved.

13 comments to Discrepancies in IDs – Hornworms – Eggs or Cocoons

  • don

    Theresa, I couldn’t read the narrative because the picture of the hornworm is right over it.The whole center portion is covered.
    Does anyone else have that?

  • Theresa

    Don, I’m so sorry you’re having trouble with this. I’ve tested two browsers and they appear alright. If anyone else has the problem I hope they’ll let me know.
    I’m working on it.

    Theresa

  • Sue

    Hi Theresa,

    I assume you do not leave the hornworm on your tomato plant. Where do you put the worm after you remove it, so it does not bother the plant?

    Thank you,
    Sue

  • Theresa

    Yes, Sue, I do leave the hornworm on the tomato plant if it has the cocoons on it. The worm won’t eat any more since the larvae have destroyed its insides. If it eats any at all – it won’t be much.

    In late fall, if the tomatoes have had blight or anything like that, I take the dead stalks and foliage out of the garden, but always check to make sure I don’t see a hornworm with cocoons. If I did, I would leave it on the garden bed. I never see them by then, because probably they’ve all hatched and moved on.

    Do you have any of the worms with cocoons?

    Theresa

  • Jen

    Hi Theresa,

    I think we just found one of these in our salsa garden. It does have the cocoons on it. So you would suggest just leaving it there? We have only seen one so far.

  • Theresa

    I would definitely suggest leaving it there, Jen.
    Hope you’re enjoying and benefiting from reading TMG.
    Theresa

  • MaryAnn

    Theresa, thanks for info about the hornworm. I am growing tomatoes on my patio for the first time and just found the cocoons on the plants. Needless to say, I was freaking out and started removing them. Now, I will leave them on the plant as you suggest. Thanks for sharing on TMG.

  • Theresa

    Hi Mary Ann,
    Glad I was able to provide this information so you would leave the hornwoms with the cocoons on them. They’ll bring you a lot more help in the future.
    I’d love to hear more about how your tomatoes on your patio are doing and what kind you are growing.
    Also, how did you find my site? It would be helpful to know.
    Welcome to TMG.
    Theresa

  • sarah

    Hi. I have been gardening for years and had never seen one of these in my garden. I found one 3 days ago and have since found 4 more. I haven’t gotten any with the white cocoons yet. Could this be a problem for me? And THANK YOU so much for the correct info. It’s been troublesome finding accurate info on this.

  • Theresa

    Hi Sarah. Glad I was able to provide the accurate information you needed. Information on this worm can be rather confusing when you’re searching and googling.
    As far as being a problem for you — that depends. You did not say whether or not you were an organic gardener. (I am.)
    If you are using chemical pesticides in your garden they can kill the braconid wasp and other good guys as well as the bad guys. If this is the case you may have killed your helpers.
    If you are an organic gardener and provide a good environment, food, shelter, and water for beneficial insects — the braconid wasp should be “on the job”.
    It could be that the wasp has laid her eggs and that they have not hatch, eaten their way out, and had time to spin the cocoon yet. What I do when I see one with no cocoons — I kill the worm and lay it on the bed just in case their are eggs in it. That way — they will have a host — although its already dead. I’ve never read this anywhere — but it’s what I do — just in case.
    You might want to read my post Hornworms – Why You might Need a Few in Your Garden
    This year I’ve seen more of these worms than in years and years! I even found two on a pepper plant the other morning. One had the cocoons. The other one did not. I left the one with the cocoons on the plant and killed the other and left him on the bed.
    Hope this helps. Let me know if you see one with the cocoons. That’ll be a good sign.

  • Robin Linzy

    I left the horn worms on my tomato plants and the about destroyed my tomato plants so I removed them.Tried to throw them away but the crawl back must be eliminated. No larva.

  • Theresa

    I only leave horn worms on my tomatoes when they don’t respond to being nudged etc. — which would indicated the eggs of the wasp are inside of them and have paralyzed their ability to eat or do anything else. And of course, if I see the cocoons I leave them.
    In my garden, the horn worm never has a chance to do much damage because the wasps take care of that.
    If your horn worms are active and “alive and well” so to speak you need to kill them or they will destroy your tomato plants.
    Don’t just “throw them away” — that doesn’t work as you already know.
    Cut them in half or throw to the ground and smush.
    Are you organic Robin?? If you use chemicals and poisons in your garden you could be killing off all beneficials that help with pest control.
    Also, you need food for the beneficials. Herbs, flowers, etc. This post might be of help to you.
    http://tendingmygarden.com/flowers-to-help-bees-help-your-garden/
    Theresa

  • Pamela Cooper

    I have 2 of these Hornworms in my Tomato garden right now. I left them alone cause they have those cocoons on them. Hope to benefit from them next year.

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