tobacco hornworm

I found this tobacco hornworm on the tomatoes the other day. I thought it was odd to see one so late in the year. Yes, it was a tobacco hornworm not tomato hornworm. The difference is that the tobacco version has diagonal lines on its side and the tomato version has v-shaped figures. One has a red "tail" the other has a darker one. Anyway, I brought it inside and put it in a jar with its attendant tomato leaves. It didn't take long for the little rascal to eat them all. Since the tomato plants did not have any more leaves to spare this time of year and after looking up its favorite plants (those in the solanum family), I decided to place a potato in his jar. Believe it or not, he started eating the potato, then I noticed his droppings also turned a light color. He feasted on this for several days and I finally added another potato and moved him to a new clean jar. He continued to eat and grow. By now I didn't have the heart to destroy him and a freeze had gotten the tomato plants, so I took him back out to the garden and released him on the remains of the tomato plant. Here, he surprised me. He started burrowing into the ground! Now, I didn't know they did this. Is that where they go to turn into the sphinx moth? We shall see......