Look how big this one was! I squished it and threw it in the compost.
The red protrusion is at the caterpillar's posterior, its head end is on the left, here.
A few weeks ago I started bringing in my potted pepper plants at night, to avoid the cold. I have my five-year-old ancho pepper plant, and have two bell peppers, one just potted up out of the garden- because the potted one I grew on the deck is leaning sideways- I kept it while the newly potted one was going through shock and to make sure it didn't bring any disease or pest into the house, before deciding which one to keep. We don't eat enough peppers, and I don't have enough winter sun space for plants, to keep all three going until spring.
Anyway- I noticed that not only was the newer pepper plant looking droopy, but it had lots of holes in its leaves. I searched for pests and didn't find any. Then one morning when moving the plant outside, I saw caterpillar frass on the floor around the plant. Around my ancho pepper plant too. I found the first hornworm that day, and disposed of it. It took a lot longer to find the other one on the ancho pepper- it was smaller. I looked a few days in a row before finding that one. Now I think I got them all because there is no more frass showing up on my floor.
Some info on hornworms from another garden blogger.