Ava Grace inspects a TOBACCO HORNWORM, aka Manduca sexta, that was devouring a ‘Cream Sausage’ tomato plant. I relocated this one, complete with a tomato leaf, to a shrub border where it will cause less damage and ultimately develop into a Carolina sphinx moth.
Only in 2020 would people get into a virtual argument over hornworms. But alas, that is EXACTLY what I found myself facing yesterday, after I posted a short video on Instagram regarding my hand removal and squishing of hornworms from tobacco and tomato plants. So, just what is all the fuss about????
First of all, I think EVERYONE can benefit from an education on just what hornworms are. The term “hornworm” is a bit misleading, as there are multiply species within the genera Manduca that make up the category that home gardeners lump into “hornworm” status. And, a quick google search proves that most of the internet does not understand the difference either!
TOMATO HORNWORM
The TOMATO hornworm, Manduca quinquemaculata, is a common garden insect that feeds on plants in the Solanaceae (nightshade) family including tomato, peppers, eggplant, and potato. Of course it is the caterpillar stage that causes the damage that gardeners have grown to hate. A distinguishing factor for identification are the V-shaped yellow and white markings on the body and the black horn, which looks scary but is totally harmless.
The adult form of the tomato hornworm is a relatively large, robust-bodied sphinx moth, commonly referred to as five-spotted hawkmoth. That names references the pairs of orange-yellow markings along the sides of its abdomen. The adult moth is in fact a “pollinator” feeding on the nectar of various flowers, typically after dark, and inadvertently moving pollen from one plant to another.
Tomato hornworm, Manduca quinquemaculata eating a tomato leaf. As i searched my vast catalog of images from my home garden I could not find a single one of a tomato hornworm. It seems I have an exclusive population of Tobacco Hornworms! Thanks to University of Florida for their excellent information and image regarding this subject.
Photograph by Paul Choate, University of Florida.
TOBACCO HORNWORM
In contrast, the TOBACCO hornworm, featured in my “controversial” Instagram video yesterday, is Manduca sexta and can be distinguished by its white diagonal lines on its body and the red horn, which is also harmless. Like their cousin, they feed on solanaceous plants, including tomatoes, and at my house tobacco, which was the crop that caught my attention.
*Side note: no, I do not use the tobacco I grow. I cultivate it to honor the heritage of the land that we live on and simply appreciate the plant for its beauty. That doesn’t mean I want it to be destroyed overnight by a pack of voracious caterpillars!
As an adult, the tobacco hornworm is referred to as the Carolina sphinx moth which has 6 yellow markings on its abdomen. The wings of both hornworm moths have a mottled pattern of gray, white, and brown resembling tree bark, which makes them practically invisible to see (or photograph) as they rest through the day.
Tobacco hornworm larvae pulled from pepper plants and offered to passing birds.
The Hornworm Video… that led to hate mail!
WHAT CAN YOU DO?
To the “haters” credit, I do love that we are living in an era where insects are finally being respected. Not that long ago most people lived by the mantra that “all bugs are bad” and that as soon as you saw one you needed to spray pesticides. Relocation of the hornworms is a more humane option, and as you can see from the video, that is exactly what I did last night when I removed a hornworm from my prized ‘Cream Sausage’ tomato plant. If you have chickens, they will happily devour every hornworm that you find- lifecycles in action.
There are a lot of different brands of Bt that are available from garden centers, box stores and online retailers.
As a home gardener who grows food for the purpose of eating it, I have to make some decisions along the way to protect my crops from insects and animals alike. After all, I am not going through the painstaking effort to cultivate tomatoes so that caterpillars can eat them. Nor do I grow cucumbers so the neighborhood fawns can have an easy access buffet. But how do you find a balance between nature (aka bugs and browsers) and nurture (aka the plants that YOU choose to grow, harvest, and eat)???? And, in this case, how then do you communicate these struggles effectively without causing an Instagram meltdown?
One option to control caterpillars is to apply Bacillus thuringiensis (Bt), a bacterium that has been used since the 1920’s and is often applied in organic farming. It naturally produces a toxin that is fatal to certain herbivorous insects including hornworms and cabbage worms. The trick is to dust the plants when the caterpillars are actively feeding because, for it to work, it has to be ingested. This can be somewhat difficult through the summer when you are watering or getting rain often, which is why I opted for hand removal when I noticed the infestation on my tobacco plants. I do use Bt on my cool season crops, like broccoli, cauliflower, and cabbage.
In past years I haven’t had to deal with this moral dilemma because the Braconid wasps arrived on time and did their job for me. But because it is 2020, and nothing is as it should be, the wasps are no where to be seen and the hornworms are quickly eating everything. Thus my decision to pick them off and squeeze them, like a 7 year old.
I love biocontrol in action! Here is a parasitized TOMATO hornworm showing the Braconid Wasp in it’s cocoon stage.
The Braconid wasp is a small non-stinging insect that kills hornworms. The female braconid wasp deposits her eggs inside the caterpillar’s body and as the wasp larvae develop, they feed on the inside of the caterpillar. Yes, it is something from a horror movie, except this is a natural cycle of life, and a very effective form of biocontrol. When the wasp larvae are ready to pupate they chew their way out of the host and spin the white silk cocoons on the caterpillar’s exoskeleton. That is what we gardeners usually see- THE LAST STAGE OF THIS REMARKABLE LIFECYCLE!
But where are my garden heroes this year? I have a feeling that the long, slow, cool, wet spring that lasted well into June is responsible for things being out of sequence this summer. At least that is what I hope. I have noticed a dramatic decline in butterflies this year as well, which has been disappointing beyond words. Fingers crossed they are just off schedule and they will arrive at some point in the coming weeks.
I was relieved to finally smell, then SEE, swallowtail caterpillars a few days ago munching on parsnip foliage. More than 2 months behind their “normal” schedule, I am hopeful that this will mean more beneficial insects will soon be arriving, and ultimately help me with this delicate balancing act of managing an organic garden that is both a sanctuary for creatures and a food source for my family.
THE REAL LESSON: KINDNESS
I hope one day to look back at 2020 and find some good from the chaos. As we are navigating these unprecedented times, it is hard to see anything positive at all, and that includes how we humans are treating each other on digital platforms and in real life. If you see something you disagree with, first consider that there is a person behind that post, who may have a valid point of view, even if it isn’t the same as your own. Then pause, and decide if it is really a fight worth having. Lastly, do what I do, and JUST KEEP SCROLLING! We do not need to battle on every single subject- there are literally bigger fish to fry than hornworms.
We can all learn so much from nature by focusing on BALANCE. Too much of anything isn’t good. Right now, I think everyone, including myself, would benefit from reevaluating the time spent on social media criticizing others. Perhaps we are all in need of some activities that will make us feel as if we have accomplished something. And that was my goal for writing this blog. I sincerely hope my experience and perspective can help you as gardeners and naturalists. Wishing you and your gardens well, Brie