Tomato Hornworm
A few weeks ago we had an inquiry concerning a large green caterpillar that was devouring a friend's tomatoes. From the description I would guess that it is a tomato hornworm. It is the larvae of the hawk moth and can grow up to four inches in length--and it can strip a tomato plant as it grows! If you have ever seen a hornworm with little white spikes on it, the spikes are the parasite of the hornworm. The adult wasp lays its eggs under the skin of the hornworm larva, they hatch and the young braconids feed on the hornworm and seals its fate. Eventually the worm shrivels. This is probably more than you wanted to know about the hornworm. In any event, the parasite is considered important in the control of the this tomato pest. However, when you discover a hornworm on your tomato plants (and they are fairly easy to detect if you follow the path of missing leaves) simply pick it from the plant and dispose of it. For a picture and more information, follow the hornworm link above!