This cool caterpillar is always found on some species of milkweed (Asclepias species). They aren't too hard to spot, with their bright stripes of black, white, and yellow. The milkweed that monarchs feed on is protected by having poisonous sap, which in turn may make the monarch caterpillar poisonous to any potential predators. Not a bad form of protection! They are brightly colored and turn into one of the most beautiful and popular of all butterflies: the monarch.