Tobacco Hornworm

I wanted to bring you an article written by one of my fellow Master Gardeners in South Carolina.  After reading Daricia's article about the Hornworms in her Charlotte Garden, I thought Ann's article would be a good companion to the other posting. 
The following article originally appeared in our MG newsletter. 

Tobacco Hornworm

By Ann Barklow

I often think of myself as an amateur research scientist when I am in the garden. When I see anything moving, I move in closer for inspection. For my research, I am never far from my 10X hand lens, laptop computer or iPhone, and camera.

Today I spotted a tobacco hornworm. I found it on my tomato plants and for obvious reasons; I was tempted to call it a tomato hornworm. You can distinguish the two by their markings. The tobacco hornworm has straight white lines like a cigarette pictured below and the tomato hornworm has “V” line markings like “vine” ripened tomatoes.

Tobacco Hornworm

If you have these large invaders in your garden in South Carolina it is most likely the tobacco hornworm. Tobacco, tomatoes, potatoes, eggplant and peppers are all in the Solanaceae family and tobacco hornworms will feed on all of them but seems to prefer tomatoes in my garden. Of course I’m not growing tobacco so I can’t speak to that.

The name hornworm can confuse you too. They do have a horn but they are a caterpillar not a worm because they are the larva of a moth. Worms are in the same form all their life where caterpillars are a stage of butterfly or moth.

The reason I spotted the hornworm was because it was covered with delicate cocoons. This was thrilling because these cocoons meant that Braconid wasps were in my garden. These parasitic wasps are only 1/10 to 1/4 inches long and are one of the most important beneficial insects that prey on aphids and caterpillars. It is one of the reasons I plant yarrow in my garden because I know they love the nectar from the flowers.

Braconid Wasp

These predators first insert their eggs in the caterpillar. These eggs hatch and the larvae begin feeding on the caterpillar’s organs causing its death. When the larvae finish, they cut their way out and spin these lovely cocoons where they pupate and turn into a wasp again and cut their way out of the cocoons. You can see their little escape hatches in the picture below. Notice the frass (insect poop) on the end under the horn. These droppings fall on the leaves below and are one of the easier ways to notice if you have hornworms since the caterpillars blend in so well. I often look for the frass and then follow up the plant and find the hornworm.

Tobacco Hornworm with Braconid Cocoons

Of course once you see one of these caterpillars you can probably find a half a dozen or more. As I looked more closely I found three more covered in cocoons and three that had no signs of attack and were eating fast and furiously. I debated for the afternoon if I should leave the ones eating so they would be available for an appetizer for newly hatched wasps but watching my plants get devoured was not easy. I have 6 very robust plants with an abundance of tomatoes and can take a bit of eating but if you only have a small patio tomato these culprits can eat it in one day! I am a big believer in biological control but sometimes it is too slow for my liking.

I decided to remove the three apparently healthy caterpillars but just in case they had wasp larvae in their bellies I placed them out into the forest a good distance from my tomato plants in hopes the wasps can complete their cycle.

This experience reminds me to continue to monitor my garden closely every day and research the critters living there. Search carefully and be sure to check undersides of leaves of your crops. If you see bugs, eggs or frass don’t ignore it. Find out what it is before it does severe damage. This can prevent a lot of discouragement and disappointment in gardening. Some of the insects you find may be beneficial like the cocoons I found. If we’re lucky nature will keep everything in balance with just a little help from us.


Thanks Ann! 

©Copyright 2011 Janet. All rights reserved. Content created by Janet for The Queen of Seaford. words and photos by Janet,The Queen of Seaford.