An American nonprofit group says the number of monarch butterflies spending the winter in the
western United States has dropped to its second lowest mark in nearly 30 years. The Xerces Society
for Invertebrate Conservation, based in Oregon, said the causes for this include the use of
chemicals to kill insects, known as pesticides. The group also blames reductions in habitat and
climate change. Monarch butterflies are known for their clear orange and black markings. They live
across North America. Monarchs in the eastern United States spend the winter in Mexico. The
World Wildlife Fund, a nonprofit based in Switzerland, counts them there but has not
yet released data for this year. Monarchs west of the Rocky Mountains usually spend the winter along
the California coast. The Xerces Society for Invertebrate Conservation has been counting
western over winter populations in California and Arizona for the last 28 years. The highest
number recorded was 1.2 million in 1997. The organization announced Friday that it counted
just 9,119 monarchs in 2024, a decrease of 96% from 233,394 in 2023. The total was the second
lowest since the survey began in 1997. The record low count was 1,901 monarchs in 2020. The survey
noted that a place in Santa Barbara that saw 33,200 monarchs last winter had only 198 butterflies
this year. Monarchs across North America face increasing threats. One is the supply of a plant
milkweed, which they feed on as caterpillars. Monarch Joint Venture is a nonprofit group based
in Minnesota that aims to protect monarchs. The group said milkweed has been disappearing
because of dry weather, wildfires, agriculture, and urban development. The Xerces Society said
pesticides might be on the remaining plants. Emma Pelton is a biologist with the Xerces Society. She
said it is unclear what caused such a sharp decrease in the western population in just one
year. The monarch population is already small, she said, and heat above 37.7 degrees Celsius in
the western states last year might have slowed breeding. Monarchs suffer when the temperature
gets up to 37.7 degrees Celsius and any temperatures above 42.2 degrees Celsius will kill
the insects, Pelton said. The western states saw a heat wave in July with temperatures in some areas
well past 37.7 degrees. Palm Springs, for example, reportedly reached a record 51.1 degrees Celsius,
on July 5th. Another heat wave hit Northern California in early October, with several cities
breaking heat records. Pelton said that it is too early to tell what long-term effect the sharp drop
might have on the overall western monarch population. Insects can reproduce very quickly,
Pelton said. After a low point of 1,901 butterflies in 2020, the population recovered to 247,246
insects the following year, an increase of nearly 13,000 percent. The year after that, the survey
recorded 335,479 monarchs. This is bad news, Pelton said of the 2024 population drop, but we have seen
incredible recovery. This doesn't mean we're not going to have western monarchs. The US Fish and
Wildlife Service announced in December 2024 that it wanted to list monarchs as threatened. Such a
move would ban people from killing or transporting them. The proposed change would also ban property
owners from making changes to their property that would make it unusable to the butterflies. For
example, removing all milkweed from a property would be banned by law. Earth Justice is an
environmental nonprofit legal group based in San Francisco. It asked the Environmental Protection
Agency in December 2024 to require testing of pesticides effects on insects such as bees,
moths, and butterflies. I'm Jill Robbins.