1. The Monarch Butterflies’ bright colors indicate to predators that they’re poisonous! This is because as a Caterpillar, they eat Milkweed. Milkweed contains a chemical called Cardiac Glycoside. Surprisingly Cardiac Glycoside don’t affect invertebrate animals or insects. But the toxic effect on vertebrates can be significant depending on the dose taken, thus keeping the Monarch’s natural predators like birds and …