You can spray with Bacillus thuringensis kurstaki (Bt kurstaki -- and make sure it's "kurstaki," because other kinds won't kill caterpillars). However, it sounds like your hornworms are so large the Bt won't help much.

Pick them off the plants. Dispose of them in your favorite manner. If you eschew violence, drown them in a jar of soapy water (but note that prying the big ones off leaves or stem is difficult). Or toss them on a driveway (or any surface that's a good contrasting color); a passing bird will appreciate the free snack.

These guys are either Tomato hornworms or Tobacco hornworms. The tobacco worms are more common; they have diagonal lines on their sides, while their tomato cousins have V-shapes. [The mnemonic is that the tobacco hornworms advertise cigarettes, while the tomato worms are ex-smokers who sport a design of broken cigs.]

Yes, the Bt will kill any other caterpillars who come into contact with it.

If you see a worm with what look like white eggs on its skin, leave it alone; those are the cocoons of a tiny predatory wasp; by the time the wasp larvae have eaten their way through the hornworm's skin and pupated, he's no longer eating. He's dead but doesn't know it. Let the wasps do their thing: the more wasps, the more hornworm-killers. And every hornworm they kill is one who can't turn into a moth and breed a new generation of caterpillars.

Condolences; I've been there (if you're very quiet, you can literally hear them chew). But faced with Late Blight, I'd rather have hornworms (in what for me so far is an oddly hornwormless year).

Here you go. Lots of info on this very common pest to browse through.

Dave

Here is a link that might be useful: Tomato Hornworm discussions

{{gwi:1379103}}

Thanks so much for the info. Unfortunately I have disposed of 2 of the caterpillars with eggs. I thought they were reproducing themselves. I will empty out my tomato planter at the end of the season and start fresh with new soil. These are some nasty little things!.