Milkweeds (Asclepsias) are native to North America, with more than a hundred species found in the US and Canada. The irritating, sticky white sap for which milkweed is named just happens to be vital to the monarch butterfly’s lifecycle. By ingesting it, they use toxins found in the sap to repel predators, creating a natural defense system.
As the sole host plant for monarchs, milkweeds provide the growing larvae with food as well as sap. Adults also feed on milkweed nectar. Without these critical plants, monarchs would have nowhere to lay their eggs, and their species would soon cease to exist.