Most tend to eat "weedy" plants, such as clover, nettles, or plantains. You can even put a green bean (uncooked) in there for it. The problem is that different butterfly caterpillars eat different foliage. They drink water, and keeping a tiny amount of it is fine, as long as the water level isn't high enough that it could fall in and drown. If you're keeping it in a container or box, keep it out of direct sunlight.
Here is a good site to go to for keeping them:
www.bbg.org
(after the .org, type in: /gar2/topics/wildlife/handbooks/butterfly guide/5.html)
Here is a good site to go to for keeping them:
www.bbg.org
(after the .org, type in: /gar2/topics/wildlife/handbooks/butterfly guide/5.html)