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.
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.
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 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.
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’!
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!
22 Replies to “Don’t Kill That Tomato Hormworm!!”
Good title for the post–it certainly caught my attention! And valuable information, too.
You are one loyal reader!
Great post! The video was fascinating, but not for the faint of heart 😉
Yes, it is nature in the raw
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.
Sara, Yes, I just read the same things. They are ‘kissing cousins’ and very closely related. Thanks for pointing this out.
So kill the tomato hookworm? Shirley Shofner
No!, If you see the worms white larvae on the worm, they are doing your work.
Ummmm… you wrote, “Once free, I stomp on these gross pests”. So yeah, you’re saying to kill them.
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.
The moth is an important pollinator, so if you have a nightshade to grow a distance away, you could move the caterpillars there
“Hummingbird” Hawk Moths are good pollinators, but shouldn’t be confused with the destructive 5 Spot Hawk Moth that produces the Tomato Horn Worm.
Yes! Thank you for saying that. It’s what I always do… no need to be cruel.
I remove them, gloves on, and throw them in the woods behind my yard. If they survive, then the moths can help pollinate my garden. If not, oh, well, but at least I don’t have to actually squash them or stomp on them. Another way to kill them, I’ve read, is to drop them in a bucket of soapy water.
I go out with a pair of scissors and execute them. That way I don’t have to touch them
Just remove them and place them elsewhere. By killing them you’re actively reducing the amount of hosts available to the beneficial braconid wasp. Just because something poses a slight inconvenience to you, doesn’t mean they don’t play an important role in the grand scheme of things.
I am telling readers to leave them alone!
How about growing extra tomato plants, or other plants in the nightshade family, just for the worms? Then the worms will become hummingbird moths which are important pollinators. We don’t have to kill (or root for the death of) every creature that inconveniences us. There can be alternatives.
I agree 100%, I remove the eggs in hopes that the caterpillar will survive. My tomato plants are 7 feet high with hundreds of leaves. I think that the moth that is produced is beautiful.
Fascinating & valuable info—thank you. In my six decades of living, I have never seen the larvae/cocoons on the tomato hornworm. And, yep, I will defend my tomato plants like nobody’s business, so when I see the hornworms, it’s off with their heads!
I ran my tomato hornworms down the garbage disposal.