A long-term study published in November had already documented the drastic decline of butterflies in Central Europe. Now a comprehensive study by Washington State University in Vancouver, USA, confirms that butterfly populations are also rapidly dwindling in North America. Between 2000 and 2020, the total number of butterflies counted declined by an average of 41.5%. Specialized species that depend on narrow ecological niches are particularly affected. A few species, however, were able to adapt and keep their populations stable or even expand them.
Butterfly decline in numbers
(© Pacific Southwest Region USFWS from Sacramento, US, Public domain, via Wikimedia Commons)
The study is based on more than 76,000 surveys from 2,500 different regions of the USA and covers 554 butterfly species. In total, more than 12.6 million butterflies were recorded. Of the 342 species with sufficient data, one third show a significant decline. Particularly worrying is that in 107 species, populations have fallen by more than 50%, while 22 species have even suffered declines of more than 90%. Overall, butterfly populations in the continental USA have shrunk by 22% within two decades. The average annual rate of decline is 1.3%. Two thirds of all species studied show a decline of more than 10%, and the number of species with shrinking populations exceeds those with growing populations by a factor of 13.
What is especially serious is that this decline can be observed almost across the entire USA. Only in the Pacific Northwest did researchers find an overall increase in butterfly populations of 10%. However, this increase is almost entirely due to a temporary population boom of the California tortoiseshell (Nymphalis californica)—a trend that is unlikely to persist in the long term. The situation is particularly worrying in the southwestern USA, where butterflies are disproportionately affected by extreme drought and rising temperatures.
These butterfly species are fighting for survival
Of the species studied, 114 showed a significant decline, while only nine species had growing populations. The monarch butterfly (Danaus plexippus), a subspecies of the Karner blue (Lycaeides melissa samuelis) and various representatives of the satyr and skipper families are particularly strongly affected.
(© Charlie Jackson, CC BY 2.0, via Wikimedia Commons)
The monarch butterfly has been at the centre of discussions around the United States’ “Endangered Species Act” for years. Its population is continuously shrinking because of habitat loss, pesticide use and the impacts of climate change. The decline of the eastern population is particularly dramatic: it has shrunk by 80% since the 1980s. The situation of the western population is even more severe, with a decline of more than 95%. Because of this alarming development, the U.S. Fish and Wildlife Service proposed in December 2024 that the monarch butterfly be officially protected under the “Endangered Species Act”.
A warning example of an already extinct butterfly species is the Xerces Blue, which disappeared in California in the 20th century because of the destruction of its habitat. Its fate could soon befall many other species.
Other butterfly species that have suffered a massive decline of more than 95% since 2000:
- Tailed orange (Eurema proterpia)
- Mitchell’s satyr (Neonympha mitchellii mitchellii)
- Painted crescent (Phyciodes picta)
- Hermes copper (Lycaena hermes)
The decline of the Florida white butterfly (Appias drusilla) is especially drastic. This species has almost completely disappeared from surveys over the past two decades and shows an annual decline of more than 40%.
Why butterflies are disappearing
The causes of the decline in butterfly populations in the USA are varied:
- Intensive agriculture and pesticide use: the massive use of pesticides, especially neonicotinoids, damages butterflies’ nervous systems and significantly reduces their chances of survival. A recent study shows that many insecticides bring barely detectable benefits for crop yields while putting pollinators and other insects at serious risk.
- Climate change: higher temperatures and altered precipitation patterns influence the flowering behaviour of many plants. As a result, caterpillars and adult butterflies often lack sufficient food sources at the crucial time.
- Habitat loss: the destruction of grasslands, meadows and wetlands, as well as increasing urbanization, deprives butterflies of their natural breeding and feeding sites.
- Regional differences: while increasing droughts in the dry regions of the U.S. Southwest cause butterflies to dry out and their host plants to wither, excessive insecticide use on agricultural land is the main threat in the Midwest.
Butterflies are not only essential for the pollination of numerous plant species, but also an important indicator of ecosystem health. Their decline is accompanied by a drastic loss of bird populations: in North America, almost three billion birds have disappeared over the past 50 years—a pattern that matches butterfly decline and illustrates the far-reaching ecological consequences.
How can butterfly decline be stopped?
Targeted conservation measures are needed to counter the decline in butterfly populations. One central strategy is to promote flower-rich habitats in agriculture, for example by creating flower strips and near-natural areas. This offers butterflies not only food, but also essential refuges.
(© Belladonna2, CC BY-SA 2.5, via Wikimedia Commons)
Drastically reducing pesticide use is equally important. Sustainable methods such as integrated pest management (IPM) or biological alternatives can help protect butterflies and other pollinators without jeopardizing agricultural yields.
Protecting existing habitats also plays a decisive role. Wildflower meadows, wetlands and unused natural areas provide valuable habitats for butterflies and urgently need to be preserved. Private individuals can also contribute by promoting native plants in their gardens and avoiding pesticides.
For migratory species such as the monarch butterfly, preserving stopover sites and overwintering areas is also essential. Without these waystations, populations are likely to continue shrinking. At the same time, political measures are needed, such as a ban on particularly harmful pesticides and a more sustainable agricultural policy, to achieve long-term improvements.
Hope for recovery
Despite the alarming figures, there is reason for hope. Butterflies have a remarkable ability to regenerate if their living conditions are improved. If targeted conservation measures are implemented consistently, many populations can not only stabilize but recover over the long term.
Measures such as restoring natural habitats, avoiding harmful pesticides and adopting more sustainable land use are particularly effective. Early successes show that targeted conservation programmes, for example for the monarch butterfly, can already have positive effects. Scientists therefore emphasize that it is crucial to act now—both locally and nationally—to give butterflies a future.
Source
- Edwards, C. B., et al. (2025). Rapid butterfly declines across the United States during the 21st century. Science, 387(1090). https://doi.org/10.1126/science.adp4671
About the author: Doreen Fräßdorf
Doreen Fräßdorf is the author and publisher of artensterben.de. She researches and writes about extinct and endangered species in the modern era, with a focus on red lists, scientific studies, historical sources, and current conservation efforts. The goal is a clear, evidence-based overview of biodiversity loss and species protection.
She is also the author of a non-fiction book about extinct modern-era mammals.
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