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Recognizing monarch butterflies under the Endangered Species Act may do more harm than good

Recent scientific evidence shows that conservation programs could harm monarch populations if done at large scales

Lila Westreich

Pollinator Ecology

University of Washington

Monarch butterflies are one of the most charismatic insects in the world. They're the most eye-catching wings in the sky, with dramatic orange-and-black coloration and a heroic migration hundreds of thousands of miles across North America. 

Insect populations are declining worldwide, and monarchs are no exception. Efforts to reverse the trends are underway across the United States and Canada. These include creating pollinator gardens for nectar sources, planting milkweed — a critical host for monarch caterpillars to acquire food and defense sources — and preserving habitats that provide shelter and nectar to foraging butterflies. Backyard gardeners, once averse to milkweed due to its weedy ability to take over gardens, are planting more milkweed than ever before. 

Even with these efforts, many national insect conservation groups advocated in 2014 for the United States to list the monarch butterfly as "threatened" under the 1973 Endangered Species Act (ESA). While the monarch wasn't added to the ESA at the time, as of 2020 the U.S. Fish and Wildlife Service announced that adding them to the ESA was warranted. But a recent op-ed from scientists at the US Geological Survey and the University of Hawai'i says that listing the monarch as endangered would be a mistake. The authors urge the US Fish and Wildlife Service to let states take their own approaches to the conservation of monarch butterflies before moving to the much more strict ESA measures.

Listing the monarch as an endangered species, the authors argue, would trigger regulatory protections that could actually harm monarch populations and current conservation efforts. Currently, there are numerous groups working to save monarch butterfly populations across North America. These include strategies by state fish and wildlife agencies to provide funding for monitoring programs, habitat conservation, and education of private landowners. A total of 27 states have included the monarch butterfly as a "Species of Greatest Conservation Need" in State Wildlife Action Plans, which allow states to use federal grant funding for personalized conservation planning. Without knowing the needs of butterflies at the state and regional level, the ESA could actually harm current efforts. 

A monarch butterfly released in Arlington National Cemetery by volunteers with Monarch Teacher Network, Sept. 1, 2015, in Arlington, VA

A monarch butterfly released in Arlington National Cemetery by volunteers with Monarch Teacher Network, Sept. 1, 2015, in Arlington, VA

Via Wikimedia

The ESA requires the designation of "critical habitat" for species listed under the federal bill, but this isn't easy for every species. Monarchs rely on milkweed and flowers on a large geographical footprint for food and the undersides of milkweed leaves to lay their offspring. It's not enough to save the monarchs by simply planting in a single area. Butterflies travel long distances across roadsides, farms, and backyards over hundreds of miles. But designating such a non-specific habitat as "critical" under the ESA could actually miss those small gardens or roadside runoff ditches of flowers that monarchs depend on for sustenance. By requiring monarch habitat in certain areas, the authors argue that larval host plants may be removed and landowners could be less interested in voluntarily planting pollinator-friendly plants on private land. Cultivating areas exclusively for milkweed may even harm other pollinators, reducing native plant availability and disrupting ecological communities.

North American monarchs can be divided into multiple groups of migratory populations, and researchers have even proposed monarchs be split into 'subspecies' across North and South America. Each population may have different needs for successful conservation, meaning that a broad approach like that written into the ESA would not help.

It's not clear if captive rearing will help either. In a recent paper published by The Proceedings of the Royal Society B., researchers found commercially derived monarchs reared outdoors failed to successfully orient south — unlike their wild counterparts. Commercially raised monarchs also changed their direction of flight more often during flight simulator experiments, and only a subset of the testing groups correctly found the southern direction over multiple tests. (On the other hand, a more recent paper from May found captive-reared monarch butterflies oriented south 26 percent of the time in flight simulators, but 97 percent of the time in the outdoors.)

A crowd of monarch butterflies at their mating site in Michoacán, Mexico

A crowd of monarch butterflies at their mating site in Michoacán, Mexico

Alex Guillaume via Unsplash

In another study, researchers found that monarchs reared in captivity had tested strength 56% less than wild butterflies. Forewing length, a trait associated with successful migration, of these indoor-raised butterflies was smaller and less elongated, and their orange coloration was paler. Darker red and orange hues in monarch wings have been linked to the ability to fly longer distances, suggesting pigment deposited on wings may be linked to thorax size, energy storage, and metabolism. 

Finally, a study from PNAS in 2019 found that captive-reared butterflies are unable to successfully migrate. Butterflies reared from eggs acquired from commercial production and wild populations were raised outdoors in enclosures over multiple generations to determine how breeding impacts hereditary traits. While wild-caught butterflies emerging in October flew south, commercial butterflies had no directionality. The commercial monarchs had smaller, rounder forewings. Indoor monarch females also had lower egg counts compared to wild females. While the environmental cues to induce migration are not well understood by the entomological community, monarchs raised indoors or reared for multiple generations in enclosures may not pick up these necessary cues, losing the ability to migrate at all.

As a kid, I used to raise monarch butterflies with my parents in our backyard. We'd collect eggs from a field near our house, and pick milkweed leaves to feed the growing caterpillars over the following weeks. Once the caterpillars had formed a chrysalis and successfully emerged, we'd bring them outdoors and release them. If you do raise a monarch this summer, make sure to tag and monitor its flight using the Monarch Watch tagging program, or a local community science project.

Later in the summer, especially during the late fall season when the offspring are responsible for making the trip south to Mexico, it may not be advised to raise butterflies in your home. Instead, plant some milkweed seeds in your yard for next season, and encourage local businesses and neighbors to plant pollinator gardens of their own. Add your data to the Integrated Monarch Monitoring Program. That way you're giving every monarch a great place to rest, drink some nectar, and continue on their way.

Comment Peer Commentary

We ask other scientists from our Consortium to respond to articles with commentary from their expert perspective.

Kristina Muise

Animal Physiology

University of Winnipeg

 Hi Lila, Great work on this article! You pulled together a lot of previously published work for this and it turned out fantastic!

My question for you is one that my supervisor always pushing me to answer when it comes to conservation, and it’s the “why should we care?”. You highlighted that monarch butterflies are one of the most charismatic insects in the world, and I completely agree with you, but why should someone care about saving monarch butterflies? Are they important pollinators, or do they feed on invasive species, or are they a key stone species? Or are they just a really cool species that gets people excited?

I’m really curious why Monarchs are favoured over other species of butterflies for conservation efforts, especially when all insects are in decline.

Derek Smith

University of Michigan

Hi Lila, I really enjoyed your article! I was wondering if you would clarify a few points for me?

I was wondering if you could expand more on how ESA regulations would inhibit individual state’s efforts. Is it because ESA funding comes with strict instructions for how it is spent? I don’t understand why funding from other sources still not be spent on other Monarch Butterfly conservation efforts at the States’ discretion.

I also don’t quite understand how the small areas of critical milkweed patches being missed by ESA sanctioned areas would harm conservation efforts. They are already being planted and maintained without ESA protection, so I would think that that should continue with an ESA protection status, unless the new ESA status prevents outside conservation efforts somehow?

Rose Egelhoff


Great article! I loved learning about how conservation isn’t one-size-fits-all. I have to wonder if one of the central ideas - that piecemeal protection may do more than a broad ESA-based conservation approach - would hold true in the eastern monarch’s overwintering grounds in Mexico, where they tend to cluster by the thousands in just a few sites.

In Mexico the conservation challenges are very different than in the U.S., but addressing them is crucial for the species’ recovery. The World Wildlife Fund studies conducted in conjunction with the Autonomous University of Mexico, found that climate change and habitat degradation in Mexico are key factors hurting the monarch population (here’s the original press release in Spanish).

In Michoacán, one of the two states where monarchs form their winter colonies, the Monarch Butterfly Biosphere Reserve is threatened by illegal logging, which is sponsored by cartels. Gangs clear land then allow avocado growers to use it, for a fee.

If we want to slow the decline of monarchs, we have to work on two daunting, international problems: climate change and Mexico’s inability to stand up to the cartels and enforce their own environmental protections. The U.S. has contributed greatly to both problems.