Monarch butterflies are on the IUCN Red List

Monarch butterflies are on the IUCN Red List

The North American monarch butterfly, whose flashy appearance and extraordinary migration have made it one of the continent’s most beloved insects, has been classified as endangered by the International Union for Conservation of Nature, the world’s most comprehensive scientific authority on the status of species.

The decision comes after decades of declining populations driven by losses in the plants they need as larvae and in the forests where adults spend the winter, combined with climate change, the assessment found. The authors reviewed around 100 studies, interviewed experts and used criteria from the group’s red list of endangered species to make their decision.

“It’s been so sad to see their numbers drop so much, so anything that can help them makes me happy, and I think that designation can help them,” said Karen Oberhauser, a conservation biologist at the University of Wisconsin who has studied monarchs in more than 35 years and contributed to the assessment. “Although it is sad that they need that help, that they have reached the point where this designation is justified.”

The number of Western monarchs living west of the Rocky Mountains fell by an estimated 99.9 percent between the 1980s and 2021. Although they retreated somewhat this year, they are still in great danger. Eastern monarchs, who make up most of the population of North America, fell by 84 percent from 1996 to 2014. The new term threatened covers both populations.

In 2020, U.S. wildlife authorities found that monarchs were threatened with extinction, but declined to add them to the list of endangered species because they said conservation of other species was a priority.

Monarch larvae depend on milkweed, the only plants they can eat. After leaving their wintering grounds, which for most monarchs are concentrated in just a few acres of forest in central Mexico, the females lay eggs on dairy plants from Texas to as far north as Canada in a multi-generational journey.

Habitat destruction in the Mexican forests was an early threat, said Anna Walker, an entomologist at the New Mexico BioPark Society who led the assessment. The Mexican government stepped in, created a reserve in 1986 and expanded it in 2000. Although there are still concerns about illegal logging and disease, this conservation effort has helped, she said, stop the overwintering habitat loss quite effectively.

But a new problem arose, the assessment noted: American farmers turned to crops that were genetically modified to tolerate glyphosate, a herbicide used in the herbicide Roundup.

“Glyphosate was suddenly sprayed over a large area of ​​farmland in the Midwest,” said Ms. Walker. “It took out many of the dairy plants that monarch larvae depend on.”

Then there are climate change, which exacerbates storms, droughts and other such events that can be catastrophic for the already vulnerable populations. Hot, dry spring seasons in the south are of particular concern to monarch experts. Add to that the broader question of climate change that disrupts old cycles, such as when plants germinate.

“We are beginning to see this kind of mismatch between when insects are ready to start spring and when the plants are ready,” said Ms. Walker. “There are lots of strangers.”

A recent study complicated the picture, and found that summer monarch abundance had declined in some areas while increasing in others, perhaps in part because warmer weather in northern areas actually helped monarchs thrive in these regions. But even these authors indicated that any silver lining could be short-lived, warning that “accelerating climate change could pose increasing threats.”

The Red List decision limits the endangered entry to migrating monarchs, which applies to those in North America. It came out of the group’s first assessment of these butterflies. The broader species includes a non-migratory variety in the Caribbean and from southern Mexico to northern South America.

The migration of the North American monarchs is considered one of the wonders of nature: small insects that fly thousands of miles north in a few generations and back in just one generation, with single butterflies flying perhaps more than 2,500 miles.

Monarch experts are eager to get the public’s help to save the species. Their message: Plant milkweed that is native to your region, which probably means avoiding tropical milkweed (it can do more harm than good, especially in the south). Swamp milkweed is an attractive, easy-to-cultivate variety that is native to all but the westernmost areas of the contiguous United States. It is for laying eggs and larvae. Butterflies need nectar, so plant native flowers that bloom when monarchs are in your area.

Dr. Oberhauser credits such interventions for helping to stabilize the population in recent years.

“We maintain a figure that is not entirely sustainable,” she said. “But if we did not have all this effort from many different organizations and individuals, I think the numbers would be even lower.”

The latest IUCN Red List update also contained bad news for sturgeon: All surviving species are now in danger of extinction, up from 85 percent of the species in 2009. The Yangtze sturgeon, a fish from China, has gone from critically endangered to extinct in wild.

Tiger figures, on the other hand, showed an increase of 40 per cent since the previous assessment, which the organization attributes to better counting combined with stabilized or increasing figures.

Emily Anthes contributed with reporting.

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