- The iconic monarch butterfly has been listed as Endangered on the IUCN Red List of Threatened Species, meaning the species is likely to go extinct without significant intervention.
- The number of migratory monarch butterflies has dropped more than 95% since the 1980s, according to counts at overwintering sites in California and Mexico.
- Renowned for their impressive migrations of more than 6,400 kilometers (4,000 miles) over several generations, the monarch decline is driven by habitat loss, herbicide and pesticide use, logging at overwintering sites in Mexico, urban development and drought.
- Experts say that planting milkweed, reducing pesticides and protecting overwintering sites for butterflies are measures needed to protect this beloved species.
The iconic monarch butterfly has been listed as Endangered by the International Union for Conservation of Nature (IUCN), a global authority on the conservation status of species. An endangered listing means the species is likely to go extinct without significant intervention.
The listing of migratory monarchs (Danaus plexippus plexippus) on IUCN Red List of Threatened Species comes as no surprise. Monarch numbers have plummeted more than 95% since the 1980s. Scientists point to climate change, habitat loss and the use of herbicides and pesticides as drivers of this loss.
“It’s been so sad to watch their numbers decline so much, so anything that might help them makes me happy, and I think that this designation might help them,” Karen Oberhauser, a conservation biologist at the University of Wisconsin who has studied monarchs for more than three decades told The New York Times.
There are two populations of migratory monarch butterflies in North America, both renowned for their impressive overland journeys spanning up to 6,400 kilometers (4,000 miles). Eastern monarchs spend the winter in Mexico, while the western monarchs winter in California. In the spring, all monarchs migrate north, some as far as Canada. This migratory cycle covers thousands of miles and takes three or four generations. Monarch population estimates are taken at their overwintering grounds.
Approximately 90% of migratory monarchs belong to the eastern population, which has been declining for decades. The area inhabited by monarchs in their Mexican wintering grounds is used as a proxy for estimating the population size. Based on these area estimates, eastern monarchs numbered around 384 million in 1996 and fell to about 60 million in 2019.
Populations of Western monarchs overwintering in California made a spectacular comeback this past winter. More than 247,000 butterflies were counted in 2021, up from a shockingly low 2,000 butterflies in 2020. However, the population has still dropped dramatically from historic numbers; more than 1.2 million butterflies were recorded in 1997.
“It is tragic to see one of the world’s most well-known butterfly species, with remarkable migratory behaviours and local cultural significance, threatened with extinction,” Sophie Ledger, a researcher at the Zoological Society of London and member of the IUCN SSC Butterfly and Moth Specialist Group, said in a statement.
Monarchs meet the criteria to be listed under the U.S. Endangered Species Act, but the U.S. Fish and Wildlife Service (USFWS) announced in December 2020 that the species would not be listed, saying that other species are a higher priority.
In June 2022, a California court ruled that invertebrates, including insects, can now be listed under the California Endangered Species Act (CESA), which may open the door for a state-wide listing of Western monarchs. An endangered listing would mean legal protections for their overwintering sites in California.
“We have seen the numbers dramatically decline over the years in our western monarch count and know this species needs our help,” Scott Hoffman Black, executive director of The Xerces Society for Invertebrate Conservation, an organization that organizes monarch overwintering counts, told Mongabay in an email. “The Xerces Society is very supportive of listing the migratory monarch as endangered and contributed expert review to IUCN for this listing.”
Monarch health is affected by habitat loss and degradation from the conversion of grasslands to agriculture, herbicide and insecticide use, logging at overwintering sites in Mexico, urban development and drought.
A Species Status Assessment Report published by the U.S. Fish and Wildlife Service in 2020 said eastern monarch populations have about a 50-70% chance of reaching a point at which extinction is inevitable within 60 years. For western monarchs, the chances are 60-68% within 10 years and 99% within 60 years. This estimate does not include catastrophic events, such as extreme temperatures. The USFWS says it will continue to focus on conservation measures along with its partners.
“Fortunately,” Black added, “there is still time to act, and we are encouraged by the thousands of individuals who have made it their mission to help monarchs by planting milkweed and nectar flowers and protecting these animals from pesticides.”
“So many people and organizations have come together to try and protect this butterfly and its habitats. From planting native milkweed and reducing pesticide use to supporting the protection of overwintering sites and contributing to community science, we all have a role to play in making sure this iconic insect makes a full recovery,” Anna Walker, a member of the IUCN SSC Butterfly and Moth Specialist Group who led the IUCN monarch butterfly assessment said in a statement.
“It is difficult to watch monarch butterflies and their extraordinary migration teeter on the edge of collapse,” she added, “but there are signs of hope.”
Walker, A., Thogmartin, W.E., Oberhauser, K.S., Pelton, E.M. & Pleasants, J.M. 2022. Danaus plexippus. The IUCN Red List of Threatened Species 2022: e.T159971A806727
Liz Kimbrough is a staff writer for Mongabay. Find her on Twitter @lizkimbrough