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The North American monarch butterfly (Danaus plexippus) is known for its long-distance migration and for its recent population decline. The U.S. Fish and Wildlife Service is proposing protection for the species and encouraging the public to take part in its recovery.
This week the service is seeking input from the public on a proposal to list the species as threatened. Public comments will be accepted on the proposal until March 12. The service will evaluate comments and any additional information to determine whether to list the butterfly.
At the same time, the California Department of Fish and Wildlife is participating in an effort by the Western Association of Fish and Wildlife Agencies to enhance western monarch conservation. Other member states—Washington, Oregon, Idaho, Utah, Arizona, Nevada and New Mexico—are doing the same. The Western Monarch Conservation Plan, adopted in 2019, looks ahead 50 years to establish population goals and habitat conservation strategies.
With its iconic orange and black markings, the monarch is one of the most recognizable butterfly species in North America. Its bright coloration serves as a warning to predators that eating it can be deadly, as its body is literally toxic. Monarchs obtain their toxins—cardenolides—by consuming milkweed plants. Milkweed produces toxins to deter animals from eating them but monarchs are immune to these toxins.
The monarch has two sets of wings spanning three to four inches. Monarch caterpillars, or larvae, have black, yellow and white stripes and reach lengths of two inches before metamorphosis. They then pupate into a green and gold chrysalis (cocoon) and emerge six to 14 days later as adult butterflies.
According to the USDA:
- A female Monarch butterfly lays from 100 to 300 eggs during her life. The eggs hatch about four days after they are laid.
- When larvae first hatch they are less than 1 centimeter and grow to be about 5 centimeters. The stages between larval molts are called instars.
- In as few as five days, the monarch develops from a pupa to an adult. The completion of the four life-stage process is called complete metamorphosis.
- The emergence of the butterfly from the pupal stage to an adult is called eclosion.
The National Wildlife Federation reports that monarchs feed mostly on milkweed, and as caterpillars they feed exclusively on the leaves of milkweed. As adults, monarchs feed on nectar from a wide range of blooming native plants, including milkweed.
The U.S. Fish and Wildlife Service’s website states that originally native to North America, the monarch butterfly has dispersed to other parts of the world and nonmigratory populations are found from islands in the Pacific Ocean to the western edge of Europe. Despite this expansion, most monarchs continue to live and migrate in North America.
North American migratory monarchs are divided into eastern and western populations. The Rocky Mountains generally divide these two populations, limiting their contact. However, the two populations are not completely isolated from each other and still occasionally interbreed. There are also nonmigratory monarchs that remain year round at the southern end of their breeding range in North America, including in parts of Florida, the Gulf Coast and California.
Michigan State University lists various reasons for the species’ decline:
- Deforestation in Mexico
- Loss of grasslands in the Great Plains’ Corn Belt
- Loss of native milkweed plants in the U.S.
- Logging practices
- Agricultural practices
- Herbicide usage
- Pesticide usage
- Climate change
- Increasing carbon dioxide levels
- Higher temperatures
The western North American migratory monarch population, generally found west of the Rockies, can migrate annually 300 to 1,000 miles. The western population overwinters in hundreds of groves along the California coast and into northern Baja California, Mexico. Monarch colonies can be found in several Central Coast spots including National Bridges State Beach in Santa Cruz and George Washington Park in Pacific Grove.
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