The signs were there. I knew I had a hornworm on one of my tomato plants. Bare branches, nibbled tomatoes, and caterpillar frass (waste) were the giveaways. The hornworm starts at the top of the plant stripping leaves and scaring small tomatoes. It can be a dreaded pest in the vegetable garden defoliating tomato plants and other plants like potatoes and peppers.
They are fairly inactive during the daylight hours so I just followed branches until I came upon it resting in the shadows of the plant.
But oh…. I saw other movement. This tobacco hornworm has company. There are siblings. Gosh, I’ve never had triplets before.
The tobacco hornworm (Manduca sexta) is identified by the red curved ‘horn,’ the soft red protrusion you can see at the tail end of the body. It also has 7 white stripes along the body. There’s a tomato hornworm with a dark ‘horn’ and white v-markings along the body.
So what am I going to do? Nothing. It’s fall. I have no tomatoes turning red. This plant is my smaller one with smaller green tomatoes. I’ll do nothing to harm the caterpillars because I admire the very last stage of development.
If you have seen the magnificent adult stage of the Manduca sexta, a large moth, darting in and out of garden blooms, you can’t help but be impressed. Its wingspan is almost 5″ and it is quite agile. It hovers over flowers and can easily be mistaken for a hummingbird. I call it a hawk moth but it’s known elsewhere as a Carolina sphinx moth and other terms.
Yep, the tomato season is over for me so I willingly offer this one plant to the caterpillars. They can be destructive but as pollinators and a food source for other organisms, they have an ecological role in nature.
It was three weeks ago that I first noticed the bare tips on a branch of a tomato plant in my small kitchen garden. I looked beneath the plant and saw some telltale caterpillar poo and I knew what was hiding on the under the leaves of my plant. I carefully lifted branch after branch until I found it… a tobacco hornworm caterpillar, the larva of the sphinx moth.
It was a gorgeous 4” long pale green caterpillar with 5 pairs of prolegs and 7 white diagonal stripes on the sides of the body and a red-colored horn on the last segment. It’s closely related to and often confused with the tomato hornworm caterpillar with similar markings but the red horn is a good identifying feature. I’ve read that tobacco hornworm is more prevalent in the southern United States and the tomato hornworm is found more in the northern states.
Both feed on plants in the nightshade family: tomato and tobacco and others such as potato, pepper or eggplant and these guys can wreak havoc in the garden and can cause extensive damage to plants. My big fellow had eaten 2 small unripe tomatoes and leaves on one small branch, however he was working alone and soon to enter the pupate stage so I left it on the plant.
Some natural bug deterrents are said to be red pepper sprinkled on the plants or a mixture of water, vegetable oil, and dish soap to repel them. Handpicking is an effective control in small gardens but one of the most common biological controls for the hornworm is the parasitic braconid wasp that lays its eggs inside the body of the caterpillar. After hatching they bore through the skin of the caterpillar and attach white cocoons along the body. If you see one with the cocoons attached, do not kill the hornworm as the wasp will do the job.
The large adult sphinx moth or hawkmoth is seen around flowers in my garden at dusk or dawn. They are as graceful and agile as a hummingbird as they hover over blooms and flit quickly from flower to flower. It’s a shame that something so full of wonder can begin life as a such a destructive insect in our gardens.
Annie, The Garden Club of Gloucester