It is that time of year when the emails and phone calls start arriving about moths: "Mr. Anderson (or Jim), I found this big green caterpillar about the size of a cigar in my yard—what is this thing!?"
In some parts of the US of A it is known as the "tobacco hornworm," but around here—with the lack of tobacco plants—it's the "tomato hornworm." In my friend Chuck Stahn's parlance, however—because it munches away on his tomato plants without conscience—it is known as "Garden Enemy #1." Just by the size, you can tell they have a prodigious appetite.
And for the record, tomato hornworms are also known to eat other plants from the family, Solanaceae: tomato, potato, pepper plants, petunias. Often, they are found on defoliated tomato plants, clinging to the underside of a branch near the trunk. (That's when Chuck gets 'em, and ends their time on Earth with one mighty blow. "Splat!")
Most of the time, however, these caterpillars are difficult to spot due to their green coloration when they're munching away, so it would be best to remove them from the plants early in the game, before said defoliation takes place and the caterpillar is small.
The organic way is to plant marigolds along with your tomatoes. Marigolds help to prohibit more than hornworms from eating your garden. An assortment of destructive beetles and moths don't like the flowers, including the pestiferous cabbage white butterflies and some cutworms.
Another method of removing hawk/hummingbird moth larvae—although not organic—is the use of a fluorescent light; they fluoresce differently from tomato leaves. Using an ultraviolet light source and viewed behind a yellow or amber filter, the hornworm fluoresces in bright green while a tomato leaf appears deep red-to-amber, and you got 'em. But, whatever you do, PLEASE DO NOT USE chemicals! Pesticides are making Earth an unfriendly place to live...
One of the reasons to stay away from chemicals is that my bees, Steve Harris's bees—or some other beekeeper's bees—will be pollinating plants in your garden and get it in the shorts.
Another reason is that native pollinators, such as bumblebees, flower beetles, male wasps and/or flower flies may also be there. The chemical you apply could have disastrous results to all of them—something you do not want to do to pollinators, no matter what! Oh, yes, hawkmoths and their kin are also wonderful pollinators as well.
During the mid-summer months, the caterpillars leave their host plants and go wandering to find the right place to burrow down in the soil, build their silken cocoon and go through that miraculous process of metamorphosis.
I call this miraculous, because to me—someone who thinks chemistry is miraculous—I cannot comprehend all that happens when the caterpillar changes from a squishy bag of green gush with one big fat body and no wings, into a completely different creature with three body parts, wings, compound eyes, six legs, all new circulatory and digestive system, completely different mouth parts that can not chew, then mate and die.
I have (reluctantly) sacrificed a moth in the process of metamorphosis and found nothing in the pupal case but green genetic soup. I assumed that was the caterpillar, broken down by some chemical process I cannot—and never will—understand, which then rebuilds itself into the adult insect. You call it what you want; I find it, "miraculous."
Now, here's a part of the hawk (hummingbird) moths that baffles me. I have photos in my library of adult moths I took in April and August. The April moths I have no trouble with. To whit: The adults lay eggs in late Aril, the host plants—let's say tomato—are on their way by this time. It takes up to 21 days for the egg(s) to hatch, which leaves all of May, June, and July for the caterpillar to grow. Then it leaves the host pant, finds a safe place underground to pupate and stays in the cocoon 'til next spring.
It's these late blooming caterpillars that throw me a curve. It takes at least two weeks for them to pupate into adults, which means they'll emerge in mid-September. By that time the tomato plants are almost done. The flying adults I have photos of from that time must find a food source to nectar on, then lay eggs. It takes about 21 days for them to hatch, and they must find some other food source, and then grow like a son-of-a-gun to be able to reach pupation to over-winter. Doesn't fit in my book; something else seems to be going on; maybe the eggs winter over...
Oh, well, there are around 1,450 species of hawk moths known worldwide, classified into about 200 genera. With Climate Change taking place (in spite of the naysayers), perhaps the hawk moths are undergoing a bit of adjustment as well as other forms of life.
In the meantime, I suggest reading Edger Allan Poe's "The Sphinx." The main character mistakenly thinks a creature he sees out a window is a huge monster. Much to his surprise, however, his friend points out it is, in fact, a Death's Head hawk moth.