The tobacco hornworm is easily confused with the closely related tomato hornworm.  Both caterpillars are the larval form of hawk moths, and both like to nibble on your tomato plants, but the tobacco hornworm has seven white lines running down each side of its body while the tomato hornworm instead has eight Vs.

Some gardeners resort to hand-picking their hornworms, while others believe that planting marigolds or basil between their tomato plants keeps the pests at bay.  I just ignore the hornworms of both types.  In our diversified environment, parasitic wasps quickly lay their eggs in each plump hornworm, and the wasp larvae eat the caterpillar alive from the inside out.  By the time these white cocoons show up on the back of the hornworm, he has long ago stopped nibbling on my tomatoes, so I am careful to leave hornworms like this in place to hatch out the next generation of parasitic wasps.

(I know I left you hanging about the tomato blight.  It turned out I had too much to say to fit in one post (surprise, surprise), so you'll hear all about it in a lunchtime series next week.)