When Not to Kill a Hornworm

Hornworm on a pepper plant leaf

 

Tomato Hornworms are really big green caterpillars that can munch through and devastate your vegetable  garden. Giant 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.

Tomato hornworm on tomato plant

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 alot. Another sign is bits of frass (droppings) on the lower leaves or on the ground which are black.

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!

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, preying mantis’s 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 worms 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 unlucky hornworm. As the eggs hatch, the larvae feed on the hornworm’s insides, eating the hornworm alive.

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

Larvae chew their way through the host skin when they mature and make a cocoon. which hatches into a tiny wasp. 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.

Leave a Reply