Large-scale farming has wiped out millions of acres of native plants, including milkweed, a vital resource for monarch butterflies—contributing to their dwindling numbers. Here’s the scoop and how you can help.
Every winter, the mountain forests of central Mexico become the home to monarch butterflies (Danaus plexippus) who travel an amazing 3,000 miles across the U.S. to reach their destination. But a report released this week by the World Wildlife Fund and Mexican government agencies warns that the number of monarchs wintering in Mexico has reached its lowest level since the migrations have been studied.
One of the primary reasons for the monarchs’ drastic decline is the widespread use of herbicides in American agriculture, which destroys milkweed plants, the monarchs’ only natural habitat and food source, in alarming numbers.
Many different species of native milkweed provide nourishment for monarchs, including swamp milkweed, green, purple, redwing, whorle and horney spider varieties. But one of the most common and numerous is the butterfly milkweed (Asclepias tuberosa).
According to the experts, milkweed sap is actually poisonous. The monarch larvae that feed on milkweeds ingest and sequester the toxins in certain parts of their bodies, which repels predators like birds (as soon as they pounce on the larvae, they quickly spit them out because of their foul taste), a biological defense mechanism monarchs keep throughout their life spans.
The offspring of monarch butterflies that lay eggs on milkweed across the U.S. will eventually fly south to Mexico. This means that it is crucial to help those that do survive over the winter by providing more food and habitat so they can reproduce come summer.
Etymologist and wildlife ecologist Dr. Douglas Tallamy says: “The more we can build monarch populations while they are in North America, the more likely the species will survive large losses during the winter months in Mexico.”
So, instead of cutting down the native plants and removing them from roadsides and fields, we can all do our part by plant more milkweed and reducing our use of detrimental herbicides.
Helping the Monarch
For more information on what you can do to foster the relationship between monarchs and milkweed, visit the website of Monarch Watch.
Joyce H. Newman, a Garden Variety contributing writer, covers gardening topics, food matters and environmental issues. The former editor of Consumer Reports GreenerChoices.org, which evaluates environmental claims on green product labels, she holds a certificate in horticulture from the New York Botanical Garden.