Once they have been parasitized, they are goners. Period. The tiny wasp lays her eggs under the skin of the caterpillar which will soon hatch into a very small wasp larvae. That larvae feeds on the internal organs of the caterpillar up until the time it is ready to pupate and complete the life cycle (turn into another adult wasp). What you see on the outside of the caterpillars are not 'eggs', but the pupal cocoons of the wasp grub. The work has already been done.

Other things prey upon these caterpillars, as well. Birds and a pretty wide assortment of predatory insects do a good job in my garden.

You might want to start looking for the caterpillar eggs, freshly deposited by the moth. Get rid of them, then you'll have no problems. I've often thought that the eggs are easier to find than the hornworms!

Those worms will grow to the size of a Volkswagen Passat, and soon invade your home. If I were you, I'd go to Home Depot and buy some plywood to shore up the windows. Did you ever watch "Invasion of the Body Snatchers?"

They're coming.........and your neighbors have already been compromised. Get out of town quick.

Look for the poop, little squares of caterpillar poop. Chances are good that the worm isn't far away.

I'm not great at squishing things, especially things as big & fat as those caterpillars. Last year, when I found them, I pinched off the leaf or stem where I found the caterpillar then took it far away from the garden and put it somewhere the birds might see it. When I went back and looked, I found no signs of caterpillars and in at least one case, the tomato branch was gone too. I didn't find them back in my garden.

(If only I could do that with the huge Black Widow that is lurking out there. She did eat a grasshopper today but still...)

Just a point of interest. The adult of the hornworm is the humminbird moth, so called because it hovers in the air like a hummingbird.
I was happy to see one of my friendly digger wasps dragging a small hornworm into her burrow the other day as lunch for the kiddies. They are also doing a number on my pickleworms.

My chickens LOVE the tomato hornworms, even the ones that are like 6 inches long. It's hilarious to see them dragging the thing across the lawn when I throw it to them :)

I toss any that I find to the robins and cardinals that always seem to follow me around in the gardens. I wonder why they do that, lol?

I found about 7 hornworms on my tomatoes last weekend. I thought deer had been nibbling the branches. I squished them and expect one of the local birds to take care of the corpses. I did not see any parasitic wasps or I wouldn't have squished them. I did notice a sphinx moth on the rhododendron bush.

Thank every one I am feeling better.
solidago1, don't worry I have tamed a snake, harnessed it and am riding into the sunset with my flame thrower , those Hornworms will never roam this land again :)