http://www.news.cornell.edu/stories/Sep ... kweed.html
Study confirms classic theory on the origins of biodiversity
"Before eating a common milkweed leaf, a newly hatched monarch butterfly caterpillar trims leaf hairs and cuts the leaf's veins to drain poisonous latex before feeding on the leaf tissue inside the circle.
Click on the image for video (Quicktime: 7 min., 50MB)"