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.

 

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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