Caterpillars on Rue Plant?

I recently bought a rue plant at a swap meet in August of 2003. A few weeks after I brought it home, I noticed what seemed to me to be possible bird droppings. So I watered the plant thinking it would wash off. Well it did not wash off; and they began to grow. Now they are taking the shape of a caterpillar about the size of my pinky finger. They are actually kind of gross. There are 5 of them and they seem to be eating my plant like crazy. I have never seen this before and hope you can tell me what they are. I know you are not an insect expert but its worth a shot. Or can you refer me to a web site where I can get this info?

You are right, I am not an insect expert and I have lent out my book on butterflies and moths and therefore cannot try to find the insect that would use rue as its host. I have tried to find an insect web-page but did not get very far. There are lots of sites that deal with rue, but not with the insects feeding on it.
I presume you are fascinated by the caterpillars and don't wish to kill them – good for you!
The possible bird droppings could have been the droppings of the caterpillars. They may have hidden and your only clue to their presence were the droppings. Now they are so big that hiding is difficult, but they should be ready to pupate soon.
Place some dry leaves on the soil surface and a few twigs into the pot so that they have a hiding place or something to hang from if that is what this species is programmed to do. If they do pupate, put the pot with them into a north window or an unheated garage and watch for the emergence of the butterflies or moths in the spring. Since the caterpillars are so large, the adult may be quite spectacular! Richters would be happy to sell you more rues to keep your future beauties well fed!
If you want help to identify the caterpillars, I suggest that you contact the zoology department of a university in your area. Likely there will be someone in the entomology section that will help you.