I'd been thinking of suckering my tomatoes, so each day I began placing my hornworm on a sucker I was glad to be rid of, and each night he'd eat two or three sucker leaves. After about four days the caterpillar was over 3 inches long (75 mm) and he was eating more every day. Just as I was running out of suckers, suddenly one night he disappeared. Either a critter ate him, or else he crawled off to metamorphose.

Naturally I assumed that this was a Tomato Hornworm. However, I wanted to scan him for my nature-study site, and during my research for writing about him I came to realize that really he was a Tobacco Hornworm, MANDUCA SEXTA. It turns out that these two hornworm species are very similar in appearance and both eat tomato plants (both tobacco and tomato plants are in the Black Nightshade Family, the Solanaceae). However, the Tomato Hornworm has a black "horn," while the Tobacco Hornworm bears a red one. You can see that my tomato-eater had a red horn.

from the September 7, 2003 Newsletter, issued from near Natchez, Mississippi:
WHITE COCCOONS ON TOBACCO HORNWORM
Earlier I reported that Tobacco Hornworms were enjoying my tomato vines, and that I'd watched a flesh fly laying eggs or larvae on a caterpillar's skin. Wednesday I noticed two more ill-looking hornworms. One had that bruised, moist look of a caterpillar who had been harassed by a flesh fly, but the other looked completely different. It was normal except that it was covered with 34 little white cocoons about 1/8 inch long (3.5 mm) and shaped like wieners. These cocoons were not made by flesh fly maggots but rather by one of many species of Braconid Wasp. That's my scanned image of the same cocoon-covered hornworm I saw at the right.

Braconids are small wasps, and you can bet that my hornworm with 34 cocoons stuck to him will not metamorphose into a sphinx moth, for recently that caterpillar has been tunneled through by at least 34 little maggots who ate much of his interior body. Braconids, along with very closely related Icheneumon Wasps, are important in controlling caterpillar populations. You may have seen them sold in gardening magazines as biological control agents.

During the last couple of weeks I haven't seen a single hornworm who wasn't obviously dying from either a flesh fly or Braconid visit. In the spring when my tomato vines were small and every leaf and bud was a treasure, I may well have presented what hornworms I found to my favorite Fence Lizards or skinks, but right now, by leaving my hornworms alone, I think of myself as feeding the Braconids and flesh flies who next year will help keep down my hornworm population.

from the August 24, 2003 Newsletter, issued from near Natchez, Mississippi:
FLESH FLY & HORNWORM
Wednesday during a late afternoon visit made to two hornworms known to be grazing a certain plant, I was surprised to find the caterpillars quiet, their heads curled beneath them. Looking closer, I saw that the larger caterpillar was blotched with dark green, moist areas, as if bruised, and that a fly was pestering it.

The fly looked a lot like a regular housefly, except that its compound eyes were conspicuously pale tan, the fly's back was striped with silvery lines, it buzzed louder than a housefly, and its aggressive behavior toward the caterpillar was very unlike a housefly's nervous manner of being. Realizing I had a different kind of fly, I got my field guides and handlens, the fly landed and remained still while I looked it over, and I determined that it was one of over 300 North American species of Flesh Fly, of the family Sarcophagidae -- a fly very different from houseflies, blow flies, tachinid flies and the rest.

Soon the fly was at the hornworm again, and this time I saw that frequently he would actually land on the caterpillar for a second or two, and that during that brief landing a tiny, white egg would be laid on the hornworm's green body. The hornworm realized that this was not good news, for again and again it bent its body around and attempted to scrape the eggs off. It couldn't reach its rear-most parts, however, or the region right behind its head, and these were precisely the bruised-looking areas, and the spots where the fly laid most of its eggs.

My fieldguide explained what was happening. Larvae from the eggs would enter the hornworm's body and tunnel through it. Eventually the hornworm would die, but not before the larvae were ready to burrow to the hornworm's skin, where they would metamorphose into adult flesh flies. Most flesh fly species are scavengers, some develop in skin sores of vertebrate animals, and a few feed on insects stored in wasp nests, but clearly here I had one of the several species who parasitize caterpillars.

n Wednesday, the hornworm, the flesh fly, the Four O'clocks, the Moonflower, the sphinx moth, and I all mingled in a congenial, interconnected, mutually sustaining permaculture ecology.