Producers: Hazel Stark & Joe Horn Host: Hazel Stark Adult monarch butterflies seek out milkweed in particular to lay their eggs. Milkweed is a native species so named for the slightly toxic milky sap that oozes from the broken leaves or stems. This diet of milkweed, which the monarch caterpillars evolved to not be harmed by, is actually essential to their survival. Photos, a full transcript, references, contact information, and more available at thenatureofphenology.wordpress.com.