Don’t Kill That Tomato Hormworm!!

Working outside I encounter a lot of unusual pests and annoyances. One of my most despised pests is the Tomato Hornworm. Tomato Hornworms are really big green alien-like caterpillars that can munch through and devastate your vegetable  garden.

Hormworm munching a tomato leaf

Nondescript brown moths lay pearl-like eggs on your tomato, pepper, or eggplant,  from which the big green monsters will hatch and start to eat voraciously. The juicy grass-green caterpillars can strip a plant overnight and then start demolishing the fruit.

Those white things on the hornworm’s body are actually cocoons, the pupal stage of the braconid wasp

Frass & Defoliation

Most of the time I spot the signs of a hornworm before I see the actual caterpillar. The first things you will notice about a hornworms presence is denuded branches and fruits with huge sections eaten out of them. Hornworms love to eat foliage and since they are such large caterpillars, they have a big appetite which means they poop all over! So watch for bits of black slimy frass (droppings) on the lower leaves or on the ground.

Getting Rid of Hornworms

Handpicking is the best way to get rid of these nasty green monsters, but I avoid touching them. With repulsive juicy caterpillars, gloves are the best option as the caterpillars usually have a death grip on the foliage and they are difficult to pick off. Once free, I stomp on these gross pests. Or feed them to the chickens for a juicy treat! But if you see white rice-like organisms on the caterpillar….. stop! Nature is taking care of the whole situation.

Beneficials

Beneficials are just that; Insects that are doing their job and preying on other harmful insects that makes your job a bit easier. For example, a preying mantis will hunt and devour lots of insects that will hurt your ornamentals and vegetables. Leave them alone to do their job!

 

So if you spot these little white wormy things sprouting out of the hormworm caterpillar, you do nothing as nature has taken care of it for you. These soft white growths are actually the cocoons of a special parasitoid wasp – a species of braconid wasp. The adult female wasp uses her ovipositor to lay eggs just under the skin of the hornworm.  When they’re ready to pupate, the braconid wasp larvae chew their way out of their host, the unlucky hornworm, and spin silk cocoons on the caterpillar’s exoskeleton. The tiny adult wasps emerge from these cocoons a short time later. Scroll down for a video of this happening.

You can see a tiny wasp that just hatched out of a cocoon

The wasps are usually dark with four transparent wings and rarely over one-half inch long. Their size and the fact that there are over 15,000 species make them difficult to notice, much less identify. So these tiny wasps are doing you a favor and killing the hornworm caterpillar by using the body as a hatching ground for their young is kind of like ‘meals on wheels’!

This is the moth which lays the eggs on foliage that will hatch into hornworms-from Wikipedia

Each cocoon will hatch a new wasp which will lay eggs in more hornworms that are eating your veggie garden, so leave them alone!

 

See this fascinating video below to see the wasps hatching out of these cocoons. Interesting and cringe worthy!

12 Replies to “Don’t Kill That Tomato Hormworm!!”

  1. From what I have read, the wasp parasitizes the tobacco hornworm, but not the tomato hornworm. Both eat tomato plants, so I believe the worm in your images is actually a tobacco hornworm. I didn’t know the difference until I google the white cocoons I had seen on one! Tobacco hornworms have diagonal lines instead of chevrons, and a curved red horn instead of a straight blue one. Just FYI.

    1. Sara, Yes, I just read the same things. They are ‘kissing cousins’ and very closely related. Thanks for pointing this out.

      1. I say that I do that if they don’t have the wasps on them. So I want them dead one way or the other but prefer nature to take its course.

  2. The moth is an important pollinator, so if you have a nightshade to grow a distance away, you could move the caterpillars there

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