These pesky caterpillars can be incredibly difficult to spot since they can camouflage into the greenery of the plants they are feasting on. However, once you’re familiar with what hornworm poop looks like, it will be much easier to tell whether you have uninvited guests in your garden!
Hornworm poop looks like miniature grenades on stems, leaves, and the soil around the infested plant. Though their color typically ranges from green to black, they may also be pinkish or reddish if the caterpillar has eaten fruits like tomato and pepper.
Do tomato hornworm and tobacco hornworm frass look different from each other? How can you tell these insects apart? I’ll teach you all about this and more!
A Sure Sign of Hornworms in the Garden: Droppings!
The poop of hornworms is grenade-shaped, with colors such as green, pink, and black. While fresh, they are slimy and soft. Once dry, they easily crumble. The pellet-sized droppings of tomato and tobacco hornworms are identical in appearance and consistency.
At a glance, hornworm poop may look like a simple speck of dust or soil, especially if it’s from a really small and young caterpillar.
When seen up close, the pellet-like droppings of hornworms highly resemble grenades due to their textured appearance. Some also liken them to corn cobs but their color can definitely affect what other things they may remind you of.
More often than not, hornworm poop is green as these insects mainly feed on the leaves of their host plants. As they dry, they can darken substantially as well.
Green hornworm poop kinda looks like broccoli florets up close. At least, that’s what I think. They can also look like tiny pink raspberries if they ate fruits from a tomato plant.
Then, if they’ve just recently fed on yellow or orange peppers, their poop will predominantly be of those shades as well. In such cases, I can see why their frass is sometimes compared to corn and pineapple.
Hornworms will release their poop grenades wherever they are. So you may find these stuck to plant stems, on top of leaves, or scattered around the soil by the base of your plant!
Needless to say, if you find hornworm poop you need to locate these green critters and discard them immediately. Otherwise, you run the risk of having completely defoliated plants!
Check our article on the 7 natural ways to get rid of tomato hornworms!
Is Hornworm Poop Good Fertilizer?
Collected hornworm poop can be used as a good fertilizer for plants in the garden. Due to their diet, primarily of leaves, droppings produced by hornworms are rich in nitrogen which is a nutrient known to promote foliage growth in plants.
Now that you’ve successfully found and removed the voracious worms from your plants, it’s best to do a little cleanup!
To be clear, this doesn’t mean you should completely discard the droppings you find. Instead, collect them all and use them to top or side-dress your plants’ soil for added nutrients. Don’t let this natural fertilizer go to waste.
A single leaf from most, if not all, plants can contain more or less 3–4% Nitrogen!
What’s even better is that the hornworm has helped you in significantly breaking down the leaf so the nitrogen in its leaf-rich poop is ready and easy for your plant’s roots to absorb.
Learn more about plant nutrients in our article on liquid and granular fertilizers!
I have also heard of others adding hornworm poop to their compost pile. Either way, it’s best to make use of such waste rather than adding it to the trash bin to do nothing in landfills.
So make the most out of the damage all those hornworms have caused in your garden by recycling their poop—which is pretty much just processed plant matter—into free fertilizer.
What about animal poop? Find out in our article on using pet poop on plants!
If you find the dead bodies of hornworms or other insects in the garden, use them to improve your soil quality as well. Just make sure that they have no pest eggs in them!
What Do Tomato Hornworms Turn Into?
In adulthood, tomato hornworms, Manduca quinquemaculata, turn into large-bodied hawk, hummingbird, or sphinx moths. They have a wingspread of 4–5 inches or approximately 10–12 cm.
If you live in the Northern region of the US and you see a green caterpillar with chevron markings on either side and a blue or black horn, you’re looking at a tomato hornworm. Oftentimes, they are confused with tobacco hornworms, but more on those later.
Let’s briefly discuss the life cycle of tomato hornworms first!
A tomato hornworm starts its life in a tiny 1-mm light green egg—which is oval in shape and smooth in texture—deposited on a leaf around springtime.
Within 1–3 days, a small white or pale yellow caterpillar will emerge and start feeding on the leaves of its host plant.
Thanks to its big appetite, the caterpillar will reach its maximum size in just 3–4 weeks. The mature caterpillar will then burrow into the soil by the base of its host plant so that it can pupate.
Under favorable conditions, an adult tomato hornworm—also known as a sphinx moth—will come out in about 2 weeks. Its wings will be a mix of grays and browns, in a mottled pattern. On their bodies, you’ll also notice 5 pairs of yellow-orange spots.
Once they’ve found a suitable mate, the cycle will repeat. They may produce 2–4 generations in one year.
What Do Tobacco Hornworms Turn Into?
Tobacco hornworms, Manduca sexta, turn into heavy-bodied Carolina sphinx moths, tobacco hawkmoths, or hummingbird moths in adulthood. They have a wingspread of 3.75–4.75 inches or approximately 9.5–12 cm.
Unlike tomato hornworms, tobacco hornworms are more commonly found in southern US regions but they can also thrive in northern states.
You can differentiate the two based on their color and markings. Tobacco hornworms have red or orange-tipped horns and diagonal white patterns with a black border on their sides.
However, tobacco hornworms share a highly similar life cycle with tomato hornworms.
The somewhat iridescent green eggs of tobacco hornworms are also about 1 mm in diameter. Young larvae then emerge from them in only 1–3 days and start feeding. When the caterpillar reaches about 80 mm in length, it enters the prepupal stage.
During this time, it will look for a good site to pupate. With an ideal site chosen, the mature tobacco hornworm will bury itself into the soil and form a reddish-brown pupa.
After that, it will pupate and emerge as a very agile moth with mottled wings in different shades of brown, black, and white. It also has 6 pairs of yellow-orange spots on its predominantly gray-brown body.
Are hornworms poisonous?
Hornworms are not considered poisonous to either humans or animals. They are not dangerous as they can neither bite nor sting. However, wild tobacco and tomato hornworms should never be fed to pets such as dogs, cats, or bearded dragons as they may contain elevated amounts of alkaloids from their diet which could be mildly toxic in large quantities.
What are the little black specks on my tomato plants?
Black specks on a tomato plant that can be easily removed with water or wiping may simply be soil or dust. Conversely, irremovable black spots on tomato leaves are which is indicative of the Septoria leaf spot, one of the most common fungal diseases in tomato plants. This can be caused by warm and humid conditions, resulting in yield loss or plant death.
Summary of What Does Hornworm Poop Look Like
A hornworm’s fresh poop is commonly green and grenade-like in shape. It’s soft and shiny if it has only been recently dropped. But as time passes, it dries up and darkens. The insect’s diet greatly affects the color of its poop; green from leaves and then pink, yellow, or orange from ripening fruits such as peppers and tomatoes.
Both tobacco and tomato hornworm droppings can be used as additional fertilizer to improve soil quality in the garden as they produce poop high in nitrogen due to their natural diets. These two species also share highly similar life cycles as they belong to the Manduca genus despite having slight differences in their physical appearance as larvae and adults.
- “Tomato hornworms in home gardens” by Jeffrey Hahn and Suzanne Wold-Burkness in the University of Minnesota Extension
- “The Hornworms Are Not Your Friends” by Kathy Keatley Garvey in Agriculture and Natural Resources, University of California
- “tobacco hornworm, Manduca sexta” by Morgan A. Byron and Jennifer L. Gillett-Kaufman in the University of Florida
- “Insects” by Hannah Burrack and Matt Bertone in NC State Extension
- “Nutrient Content of Plants” by n/a in the University of Georgia