Hornworm

Easily recognized by their unusually large size (up to 4”) and horn-shaped tail, tomato hornworms (Manduca quinquemaculata) can strip your tomato plants of foliage and fruit in short order. 
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Distinguished from their tobacco-loving cousins, Manduca sexta, by displaying white V-shaped markings, rather than single slash marks, both varieties are difficult to see until the damage is done. To learn more about the differences between these two agricultural pests, the University of Florida Extension Office has an excellent resource.

Tomato hornworm

Hornworm damage

The first sign of hornworm infestation is usually stripped leaves and missing smaller stems on tomato plants. Hornworm caterpillars will also eat peppers, potatoes, eggplant and even jimsonweed ~ all members of the nightshade family. They prefer younger, new growth, but they tend to hide under larger leaves. Their bright green coloration provides excellent camouflage. 

Once they eat their fill of your garden delectables, hornworm caterpillars will return to the soil where they develop a hard-shelled pupal covering. Within their winter chalet, hornworms undergo a complete metamorphosis from worm to moth. In spring, the large (4-5”), heavy-bodied brown Sphinx moth will emerge to lay light green, oval eggs on upper and lower leaf surfaces. These eggs hatch and tiny caterpillars emerge, and the cycle continues. In some cases, a second generation can occur in a single year.

Tomato hornworm moth (Wikipedia) CC BY 3.0

So what can you do if you find hornworm damage on your plants?

Handpicking hornworms from your plants is the best defense. They can be dropped in soapy water, tossed in a trash bag or, my favorite, fed to the chickens! Plants should be inspected at least twice a week through summer. If you happen to be lucky enough to discover a hornworm covered with little white packets, do yourself and your garden a favor: place the hornworm in a container covered with hardware cloth and leave it alone. The little white packets are the eggs of predatory braconid wasps. These beneficial wasps are too tiny to cause humans any problems, but they are your friends in the garden. As they hatch, they will feed on the hornworm body, as nature intended.

Since hornworms also feed on weeds in the nightshade family, you can reduce hornworm populations by keeping your garden weed free. Also, in the fall, till the soil where susceptible plants were grown to kill pupae and burrowing caterpillars.

Green lacewings and lady beetles also prey on eggs and new caterpillars, so keep your garden predator-friendly with water, plants from the Allium family, and little or no pesticide use.