While watering my tomatoes this morning I noticed a few roundish black droppings on a tomato leaf. I know, from many years of tomato growing, to suspect a leaf-eating caterpillar in the presence of such droppings. I had to look closely, just above the leaf where the droppings rested, and there it was.
The first hornworm of the season. (I removed the leaf, hornworm and droppings included, for the sake of this photo.)
It had only done minimal damage, but left unchecked it could have defoliated the entire upper branch structure of the potted tomato. Hornworms voraciously munch on tomato leaves. They are so well camouflaged, assuming the same color of a tomato leaf, that it’s difficult to locate them until they are much larger.
The only time to leave a hornworm in place on a tomato leaf is when it is covered by tiny, white, oval egg casings … the sign of a parasitic wasp that uses a hornworm body as a breeding/gestation ground for the next generation of wasps. Youngsters hatch out of the casings and feed on the guts of the hornworm before transforming into parasitic wasps like their parents.
I know, this sounds gross. But it’s not nearly as appalling as the sight of mature tomato plants with leaves munched to their veins by adult hornworms. Left unchecked, hornworms will totally defoliate a mature tomato in just a couple of days.
It takes a sharp eye to find them, though. When young and small, they are often at the edges of tomato leaves. When more mature, that is more full of your tomato leaves, they often rest along stems, like in the photo below from my 2010 garden.
Always look for hornworms when you see tiny roundish droppings, like those on the leaf surface in the photo at the top of this page, on or just below a tomato leaf.
If you cannot tolerate leaving a hornworm in place, munching away while waiting for parasitic wasps to find it as a host for egg laying, then hand-pick any hornworms you find and drown them in a jar of water, lightly soaped (dish detergent). Or, if you’re not the squeamish type, squish them.
But, before destroying any hornworm, take a moment or two to admire their coloring. They can be truly beautiful, intricately-patterned, almost other-worldly creatures.