Milkweed is a plant that many gardeners consider to be a pest. It grows quite tall and is not very pretty. Also, it spreads quickly and crowds out other plants. Milkweed gets its name from the milky juice that it produces. This juice contains alkaloids, latex, and other substances. Some species of milkweed are toxic to humans, so the plant should not be eaten. However, the sap of the milkweed has sometimes been used externally as a natural remedy for poison ivy.
Although the milkweed may seem to be a nuisance to many people, it is very beneficial, and even essential for some insects. The nectar and pollen that insects get from the flower do not contain poisonous substances. Therefore the insects can eat them safely. Many types of insects feed on the nectar and collect the pollen of the milkweed. These include bees, wasps, moths, and butterflies. These insects are also very important to the milkweed. Without them the milkweed would not be pollinated and thus could not survive.
Milkweed also provides a hiding place for some insects. According to a USDA website, one can find milkweed growing along roadsides and in pastures, soybean fields, corn fields, and on “land maintained in the Conservation Reserve Program (CRP) of the USDA Natural Resources Conservation Service.” Yellow jackets eat bees and flies that get trapped in the milkweed flowers. Also, crab spiders hide on it to prey on unsuspecting insects that come to visit the plant.
There are several insects that would not survive without the milkweed. One of these is the beautiful monarch butterfly. The caterpillar of the monarch butterfly will eat only milkweed. This caterpillar is not harmed by the cardiac glycosides found in the leaves of the plant. The cardiac glycosides go into the body of this caterpillar and make it poisonous. This effect protects the caterpillar from predators. Even after the monarch has become an adult butterfly, the glycosides remain in the body and protect it from being eaten.
In addition to the monarch butterfly, Milkweed Bugs and Milkweed Leaf Beetles will eat only milkweed. If there were no milkweed, they could not survive.
Most animals cannot eat milkweed because the cardiac glycosides are poisonous to them. However, many animals, such as birds, feed on insects. Those moths and butterflies that eat only the nectar of the plant are not poisonous to their predators. Therefore both the insects and their predators are benefited by the milkweed plant.