I think it's a white-lined sphinx moth caterpillar. The caterpillars of this species have many different forms.

You could have some fun and finish raising it yourself. The link should have the information about how to do it, but I'm pretty sure all sphinx moths go underground to make their pupa, after they've finished the last instar and are through eating. You could give it a container full of clean leaves to burrow in for that.

Check out the link and see what you think.

Sherry

Here is a link that might be useful: White-Lined Sphinx Moth

Thanks Sherry. Looks like it is a white-lined sphinx moth cat from the link. I don't really want to raise the little fellas myself, I'll just let them carry on on their own. I have seen sphinx moths around here and I dig up their pupae by accident all the time (I rebury them). Such cute, chubby guys!

Karen