Interactions with other organisms

Since the common milkweed has a vast geographical and ecological range throughout North America, there are many organisms it comes in contact with. One organism that common milkweed has a relationship with is the monarch butterfly. In the spring, adult monarchs lay eggs on many species of milkweed plants including Asclepias syriaca. The eggs hatch and become caterpillars as we know them, which is the larval stage of the monarch butterfly. The caterpillar spends its life on the plant; it will eat the leaves in order to undergo rapid growth. Milkweed is the only plant it relies on. To reach the adult form, the caterpillar forms into a chrysalis on the milkweed plant and will eventually reach the adult butterfly stage. This whole process occurs in about one month. The adult butterfly will continue to feed on the milkweed plant, but it now will eat the flowers rather than the leaves(National Parks Service). Since milkweed is toxic, the butterfly is protected from predators by eating the plant. This interaction can be seen in the pictures on this page. Another species the monarch butterfly interacts with is hot peppers. Read more about the monarch butterfly and milkweed at www.nps.gov/ or monarchlab.org

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Many other critters, such as the Delaware skipper, milkweed beetles, and bumble bees can also be found on milkweed. Some of them, such as the bees, pollinate milkweed.

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One study found that grasses that grew in close association with milkweed limited milkweed’s growth due to competition for soil resources and competition for sunlight to perform photosynthesis. Also, at the same time, the milkweed was in contact with a beetle that ate at the roots of the plant which caused shortages in the growth during the early part of the growing season (Agrawal, 2004). This study shows that there are organisms that can inhibit the success of Asclepias syriaca, but from other studies, we also know that milkweed has some negative effects on other organisms. You can read about the toxin found in milkweed on the facts page.

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