Low number of monarch butterflies concerns experts

Conservationists are concerned that western monarch butterflies may be teetering on the brink of collapse as the latest Western Monarch Count reveals a devastating decline. The 28th annual survey, conducted by the Xerces Society on Jan. 30, recorded the second-lowest overwintering population since the count began in 1997, deepening fears for the species’ survival.

Despite the stark numbers, experts urge the public not to lose hope. “I really want to spread the word that we should not give up right now,” said Isis Howard, a conservation biologist with the Xerces Society. In 2020, the monarch butterfly population dropped to an alarming low, with fewer than 2,000 butterflies counted across California. However, the following year, their numbers rebounded to over 200,000, showing that recovery is possible. Still, their future depends on favorable conditions.

This winter’s mid-season count — conducted at 257 sites by 400 volunteers — tallied just 9,119 monarch butterflies, a stark contrast to the 1980s, when millions overwintered along the California coast. The all-time low was recorded in 2020, when fewer than 2,000 monarchs were counted statewide.

Some of the largest clusters this season were found in Santa Cruz County, with 1,406 monarchs at Lighthouse Field State Park, 1,400 at Natural Bridges State Park and 645 at Moran Lake. However, in Pacific Grove, a historically significant site, the count plummeted to just 228 monarchs from 15,960 recorded in 2022 according to the data by Xerces Society. In January 2024, volunteers discovered several hundred dead and dying monarch butterflies near the Pacific Grove Monarch Sanctuary, a key overwintering site for the species.

Why are monarchs in decline?

The western monarch butterfly (Danaus plexippus) is one of North America’s most iconic insects, known for its extraordinary migration from summer breeding grounds to overwintering sites in California and Mexico. During the spring and summer, the adult monarchs spend their 2–5 week lifespan mating and slurping the nectar on flowers, with females searching for milkweed upon which to lay their eggs. Over 3-5 generations of western monarchs are produced during this time, with the final fall generation migrating to overwintering sites in Mexico and California where they live for 6-9 months.

Once numbering in the millions, western monarch populations have declined by over 95% in California and 80% in Mexico, according to the Xerces Society. Over the past 40 years, their numbers have fluctuated wildly — from a few hundred thousand to a few thousand — making long-term trends difficult to predict.

Experts cite climate change, habitat loss, and pesticide use as the primary drivers of decline. However, pinpointing the exact causes of year-to-year fluctuations remains a challenge.

In January 2024, volunteers found several hundred dead and dying butterflies near the Pacific Grove Monarch Sanctuary. According to the Xerces Society, tests confirmed that monarchs in Pacific Grove were exposed to multiple pesticides, including lethal levels of man-made pyrethroid insecticides, likely from an unreported local source.

“The problem is that we do not know what the numbers mean,” said Arthur Shapiro, professor emeritus of evolution and ecology at UC Davis. Scientists also don’t fully understand where they’re wintering and breeding, which may be shifting due to climate change.

Shapiro suspects that changes in seasonal temperature and daylight alignment — especially nighttime temperatures — are disrupting monarchs’ migration patterns.

How you can help

In 2020, the monarch population fell to an all-time low, but the following year, numbers rebounded to over 200,000, proving that recovery is possible. However, scientists emphasize that their future depends on widespread conservation efforts.

“As of December, the U.S. Fish and Wildlife Service has proposed listing monarchs as a threatened species under the federal Endangered Species Act,” said Emma Pelton, a senior conservation biologist at Xerces. “The good news is there are a lot of ways for people to help monarch conservation.”

According to the Xerces Society, scientists attribute the decline of western monarch butterflies to factors such as widespread pesticide use and the loss of both breeding and overwintering habitats. By identifying local species of milkweed and nectar plants, and sharing this information with friends, people can contribute to monarch conservation. Joining community science projects like the Western Monarch Milkweed Mapper and making donations to the Xerces Society are other effective ways to help. Individuals can also adopt a local overwintering site, volunteer, and advocate for its protection.

Despite their recent struggles, monarchs have proven resilient. Given the right conditions, they can rebound. However, action is needed now. “People should not give up, because these species are bouncing around in uncharted territory, but we really need all hands on deck,” Howard said. “One of the special things about monarchs is that everyone has a role to play in monarch conservation.”