If you grew up seeing monarch butterflies drift through your backyard in late summer, you may have noticed that happens a lot less often these days. That’s not your imagination. Eastern monarch populations have fallen by more than 80 percent since the 1990s, and western populations have fared even worse, collapsing by over 95 percent in the same period. A butterfly that once traveled the continent in vast numbers is now listed as endangered on the IUCN Red List. Understanding why monarchs are in trouble – and what can actually be done about it – starts with looking honestly at the pressures they face from multiple directions at once.
Key Takeaways
- Monarch populations have declined more than 80 percent since the 1990s, driven by the near-elimination of milkweed from agricultural landscapes through widespread herbicide use.
- The oyamel fir forests in central Mexico where monarchs overwinter have lost roughly half their cover to illegal logging and land conversion, removing the critical thermal buffer monarchs depend on to survive winter.
- Climate change is disrupting the timing of milkweed growth, migration, and overwintering conditions in ways that create mismatches monarchs cannot easily adapt to on their own.
- Planting native milkweed species and pesticide-free nectar plants remains one of the most direct, evidence-backed actions individuals can take to support monarch recovery.
Milkweed Loss From Herbicides
Monarchs can only lay their eggs on milkweed. Their caterpillars can only eat milkweed. Without it, there is no reproduction, no next generation, and no migration. That simple biological dependency is at the heart of the monarch’s decline.
For most of the twentieth century, milkweed grew throughout the corn and soybean belt of the Midwest as a common field weed. Farmers dealt with it, but they couldn’t fully eliminate it. That changed in the late 1990s when genetically modified herbicide-tolerant crops became widely adopted. Farmers could now spray glyphosate directly over entire fields at any growth stage without harming the crop. The result for milkweed was devastating. A study published in Insect Conservation and Diversity estimated that over a billion stems of milkweed disappeared from agricultural fields in the Midwest between 1999 and 2010 alone. That’s not a slow erosion. That’s an elimination.
The Midwest matters so much because it historically produced the majority of the eastern monarch population. Summer breeding monarchs move north through Texas into the corn belt, where dense milkweed patches once supported explosive population growth each year. With that milkweed largely gone, the summer breeding surge that used to fuel fall migration numbers simply doesn’t happen at the same scale anymore.
Roadside and utility corridor milkweed has picked up some of the slack, but not enough. Mowing schedules, herbicide spraying along right-of-ways, and the fragmented nature of these corridors all limit how many monarchs they can support. Urban and suburban gardens help too, but the sheer scale of agricultural milkweed loss is not something backyard plantings can fully compensate for on their own.
Monarchs have remarkable biological adaptations that have helped them survive for millions of years, but those adaptations evolved in a world where milkweed was abundant. They don’t help when the food source itself disappears from the landscape.
Habitat Destruction at Overwintering Sites
Every fall, eastern monarchs travel thousands of miles to a tiny cluster of oyamel fir forests in the mountains of Michoacan and Mexico State. These forests sit at elevations between about 10,000 and 12,000 feet, where the climate creates a precise set of conditions – cold enough to slow monarchs’ metabolism and reduce fat consumption, but not so cold that they freeze. The trees themselves hold moisture and moderate temperature swings in ways that no other site in the region replicates. The monarchs don’t just prefer these forests. They need them specifically.
The problem is that these forests have been under sustained pressure for decades. Illegal logging operations have cleared significant portions of the core butterfly reserve, along with adjacent buffer zones. Legal and quasi-legal land conversion for agriculture and development has contributed further losses. The Mexican government and conservation organizations have worked to curb logging within the reserve boundaries, and enforcement has improved in recent years, but the damage already done has reduced forest cover substantially.
When forest cover is lost, the thermal buffering breaks down. Open areas within the forest expose overwintering clusters to temperature extremes that intact canopy would otherwise moderate. A severe cold snap with rain can kill millions of monarchs in a single night if they are roosting in degraded habitat. This happened dramatically in 2002, when an ice storm hit an already-fragmented overwintering site and killed an estimated 500 million monarchs in a matter of days.
Western monarchs face a parallel problem along the California coast. Their overwintering groves, concentrated around Pacific Grove, Santa Cruz, and Pismo Beach, have been lost to coastal development, eucalyptus removal projects, and changes in the microclimates those groves provide. The western population, which once numbered in the millions, dropped to fewer than 2,000 individuals counted at overwintering sites in 2020 before recovering somewhat in subsequent years. That recovery is encouraging, but it illustrates just how close to collapse these populations can get.
Climate Change Effects
Climate change layers additional stress on top of the habitat problems, and it does so in ways that are harder to address through direct action. The effects are not just about temperature going up. They’re about timing, predictability, and the synchrony between monarchs and the resources they depend on.
Milkweed growth is triggered by temperature and moisture. Monarch migration timing is controlled by day length and temperature cues. When spring arrives earlier than it used to, milkweed may emerge before monarchs heading north from Mexico are in position to use it. When fall temperatures stay warm longer, monarchs may delay southward migration and arrive at overwintering sites with depleted fat reserves. These mismatches – ecologists call them phenological decoupling – reduce breeding success and survival in ways that compound existing population pressures.
Drought is another factor. Milkweed plants stressed by drought produce less leaf tissue and fewer flowers, reducing both larval food and nectar availability for adults. Severe drought years in the southern United States can effectively shut down the spring breeding pulse that monarchs need to rebuild numbers after winter. The increasing frequency of extreme drought events in the central and southern United States is a direct threat to this part of the monarch life cycle.
The overwintering sites in Mexico are also projected to shift or shrink under climate change scenarios. Research published in PLOS ONE modeled how rising temperatures at high elevations in Michoacan could reduce the area of suitable overwintering habitat significantly by mid-century. If the forests warm beyond the threshold monarchs need for winter dormancy, the entire overwintering strategy that eastern monarchs have relied on for thousands of years could be disrupted in ways that no conservation effort can easily counteract.
Understanding the full scope of the monarch’s journey helps put these climate threats in context. The mysteries behind monarch migration reveal just how finely tuned this system is – and how many things have to go right across three countries for the migration to work.
What Is Being Done
Conservation efforts for monarchs are genuinely multifaceted, and some of them are showing results – even if the overall picture remains concerning.
In Mexico, the Monarch Butterfly Biosphere Reserve has been in place since 1980, and enforcement against illegal logging has tightened over time. Community forestry programs that give local ejido communities economic incentives to protect forest rather than log it have had real success in some areas. The reserve was expanded in 2000, and ongoing monitoring tracks forest cover annually. The Mexican government also launched a national strategy for monarch conservation that coordinates across federal agencies.
In the United States, federal agencies including the U.S. Fish and Wildlife Service have developed monarch conservation plans, and the species came close to receiving Endangered Species Act protection in 2020 before being labeled a “candidate” species – meaning it qualifies for listing but was deprioritized due to competing listing needs. ESA listing, if it happens, would require federal agencies to avoid harming monarch habitat on public lands and could restrict some uses of private land as well.
Agricultural programs through the USDA have funded milkweed planting and pollinator habitat restoration on farmland through programs like the Conservation Reserve Program. Highway departments in some states have shifted mowing schedules on roadsides to allow milkweed to grow and set seed before being cut. Several large landowners and corporate farms have enrolled in voluntary monarch habitat commitments through programs managed by the National Wildlife Federation and the Monarch Joint Venture.
Research into captive rearing and population genetics is ongoing, though the scientific consensus is that captive breeding is not a realistic solution at the scale needed. The monarch population is simply too large, and the genetic diversity too important, for captive programs to substitute for wild habitat. The Center for Biological Diversity has been an active legal advocate for monarch ESA listing and continues to push for stronger federal protections.
How You Can Help
Individual action matters more for monarchs than for most endangered species, because the main limiting factor – milkweed – is something gardeners and landowners can actually provide. You don’t need a farm to make a difference.
The most important thing you can plant is native milkweed. The species that are native to your region are almost always better choices than tropical milkweed (Asclepias curassavias), which can harbor a parasite called OE (Ophryocystis elektroscirrha) at higher rates when it stays green year-round in warm climates. Common milkweed (Asclepias syriaca) in the Midwest, butterfly weed (Asclepias tuberosa) across the East, and showy milkweed (Asclepias speciosa) in the West are all excellent options depending on where you live. A detailed guide to caterpillar host plants for gardeners covers milkweed species selection and growing tips in depth.
Beyond milkweed, monarchs need nectar sources throughout the season – especially in late summer and fall when migratory adults are building fat reserves for the journey to Mexico. Native asters, goldenrod, ironweed, and Joe Pye weed are among the best fall nectar plants in eastern North America. Avoiding pesticides, including systemic neonicotinoids used as seed coatings or soil drenches, is equally important. Even nectar plants treated with these insecticides can harm monarchs that feed on them.
If you have more land available, consider creating a certified monarch waystation through Monarch Watch’s waystation program. The program provides guidance on plant selection and garden design, and your waystation becomes part of a mapped network of monarch habitat across North America. The more connected these habitat patches are, the more effectively they support monarchs moving through on migration.
You can also support monarch conservation through advocacy. Contacting your congressional representatives about Farm Bill conservation funding, supporting state programs that protect roadside milkweed, and pushing back against indiscriminate herbicide use in your community all have cumulative effects that scale beyond your own garden.
FAQ
Are monarch butterflies actually extinct yet?
No, monarchs are not extinct. They are, however, classified as endangered on the IUCN Red List as of 2022, reflecting serious population decline. The eastern migratory population has fallen by more than 80 percent since the 1990s, and the western population has declined even more sharply. While monarchs can still be found across much of their historic range, the population size is a fraction of what it once was, and scientists consider the species at significant risk of further decline without meaningful habitat restoration.
Why is milkweed so important for monarchs specifically?
Milkweed is the only plant group that monarch caterpillars can eat. Female monarchs will only lay eggs on milkweed plants, and the larvae must consume milkweed leaves to grow and survive. Milkweed also provides monarchs with cardenolide toxins that they sequester in their bodies, giving adults chemical protection against predators. There is no substitute plant that fulfills these roles. This means that wherever milkweed disappears from the landscape, monarch reproduction disappears with it.
Can planting tropical milkweed hurt monarchs?
In warm climates where tropical milkweed stays green year-round, it can create problems. The plant can encourage monarchs to skip migration and overwinter locally, which disrupts the migration instinct over time. More importantly, non-migratory monarchs on year-round tropical milkweed accumulate higher loads of OE (Ophryocystis elektroscirrha), a debilitating protozoan parasite. In climates where tropical milkweed dies back naturally in winter, these risks are much lower. In frost-free zones like Florida and Southern California, cutting tropical milkweed back to the ground in fall or replacing it with native milkweed species is strongly recommended by most monarch researchers.
How many monarch butterflies are left?
Population estimates vary depending on the method used. The eastern population is typically measured by the area of forest occupied at overwintering sites in Mexico. In recent winters, that has ranged from about 2 to 7 hectares, compared to peaks of over 20 hectares in the 1990s. Each hectare of occupied forest is estimated to hold somewhere between 10 million and 50 million butterflies, making precise total counts impossible. The western population is counted individually at California overwintering sites and has ranged from under 2,000 to around 300,000 in recent years, with considerable variation between seasons.
What is the single biggest threat to monarch butterflies?
Most researchers point to milkweed loss as the primary driver of eastern monarch decline, based on the correlation between herbicide-tolerant crop adoption in the Midwest and the steep drop in overwintering population numbers that followed. However, the threats monarchs face are interconnected, and isolating a single cause oversimplifies the situation. Habitat destruction at overwintering sites and climate change both contribute meaningfully, and addressing any one threat in isolation is unlikely to be sufficient. Recovery will require simultaneous progress on milkweed restoration, overwintering site protection, and reducing climate-driven disruptions to migration timing.
