The Tomato Horn Worm can do a tremendous amount of damage to your tomato plants.  This strikingly marked caterpillar will chew the leaves and the fruit of your tomato plant.  The Tomato Horn Worm will often eat the entire leaf and stem right down to the main branch.  This photo shows damage that is typical of the Tomato Horn Worm.  Notice the branch looks bare and stripped of leaves. Larger tomato horn worms will chew the tomatos themselves, leaving them ruined and useless.

Photo Copyright: Brad Sylvester, all rights reserved

If you see this type of damage to your tomato plants, look more closely for the Tomato Horn Worm.  Tomato Horn Worms can be manually removed from the plant and destroyed when found.  If the tomato horn worm starts eating the tomato fruit itself, it looks like someone took a razor sharp spoon and took shallow scoops from the top of the tomato. The caterpillar will hang down from the stem above the tomato fruit and eat as much as it can reach without having to move.  Often if there are several fruits on the branch, each one will have a few scoops as the caterpillar swivelled it's head from one to the other.

The Braconid Wasp Helps Control Tomato Horn Worms

The Braconid Wasp will also help control Tomato Horn Worms organically.  The braconid wasp will lay its eggs on the Tomato Horn Worm and the Wasp larvae will consume the Horn Worm.  Here is a picture of a parasitized Tomato Horn Worm.

Each of the protruding white cylinders is the pupa of a braconid wasp.  When they emerge from the pupae, they will seek new Tomato Horn Worms on which to lay their own eggs.  If you find Tomato Horn Worms in this condition in your garden, you may choose to leave them alone. The hatching braconid wasps will multiply and help you hunt down and destroy any remaining tomato horn worms under control. Typically when you see a tomato horn worm that has been parasitized by the braconid wasp, it will be much smaller than healthy peers.  I haven’t seen parasitized horn worms bigger than 1.5-2” in length.  They are also usually thinner as is evident in the one pictured above.  Obviously this is because the braconid larvae are consuming the tomato horn worm and it doesn’t have the energy or resources to maintain its weight or to grow much if at all.  Healthy tomato horn worms can be as long as four inches and are quite plump. The good thing about this is that it is the oldest and largest stage of larval development in which they have the biggest appetites and do the most damage to your garden. If they fall victim to the braconid wasp, they never get that big and damage is greatly reduced.

Life Cycle of the Tomato Horn Worm

The tomato horn worm is the larval form of the five spotted hawkmoth, Manduca quinquemaculata. You can see a picture of the adult moth here at wikimedia. The adult five spotted hawkmoth has a wingspan of up to five inches, but most of those we see around Sylvan gardens tend to be in the range of a 3-4" wingspan.  It’s still one of the larger common moths, though it's nowhere near the size of the luna moth. The male and female are pretty similar and you most likely won’t be able to tell them apart without capturing them and examining them closely. The female lays her eggs on the leaves of suitable host plants which the hatching caterpillars (Tomato Horn Worms) will eat. The eggs may be laid on the top or bottom of the leaf. They are little green ovals between one and two millimeters in diameter.  Occasionally they will be closer to white in color.  (Editor’s note: I’ll add a picture of the eggs here as soon as I find more in the garden. 8/22/08) The five spotted hawkmoth’s eggs take at least a couple days to hatch, and I’ve seen them take more than a week before hatching. When the tomato horn worm reaches full size, it burrows into the ground where it forms a pupa. It is here that the metamorphosis into an adult five spotted hawkmoth will occur.

-More information and photos coming… (last updated 9/16/08)

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