Butterfly numbers plummeting in US west as climate crisis takes toll

Butterfly numbers plummeting in US west as climate crisis takes toll

The varied, and beautiful, butterfly species that dot the US west are being cut down by the climate crisis, new research has found, with rising temperatures helping cause a steep decline in butterfly numbers over the past 40 years.

There has been a 1.6% reduction in the total number of butterflies observed west of the Rocky Mountain range each year since 1977, researchers calculated, which amounts to a staggering loss of butterflies over the timespan of the study period.

“You extrapolate it and it feels crazy but it’s consistent with the anecdotal ‘windshield effect’ where people aren’t spending time cleaning insects from their car windshields any more,” said Matt Forister, biology professor at the University of Nevada and lead study author.

“Certainly many butterfly species are becoming so rare it’s hard for some people to see what were once widespread, common species.”

The declines are winnowing away much-loved species such as the monarch butterfly, which is known for is spectacular mass migrations to California each year but has lost 99% of its population compared with 40 years ago. “With the monarch it seems we are on the verge of losing the migration, if not the species itself,” Forister said.

The research, published in Science, analyzed citizen-gathered sightings of butterflies in 72 locations spanning all of the western US states. In all, more than 450 butterfly species were included in the study.

Across all of these sightings, the researchers found an annual 1.6% drop in butterfly numbers in the west, which is consistent with the rate of decline of other insects found by researchers in different places around the world, fueling concerns of a deep crisis among the creatures that help supply much of our food, break down waste and form crucial foundations to the web of life.

While butterflies, like other insects, are being negatively affected by habitat loss and toxic pesticide use, the researchers accounted for these factors in their study and found that the heating of the planet, even without those other pressures, is causing the steady decline of butterflies.

This could be because plants are drying up more rapidly at the end of summer, meaning nectar resources are more scarce for butterflies, or that warming winters are interfering with the stasis-like state butterflies enter during colder months, meaning they are in worse condition when spring arrives.

“We have a lot of wide open land in the west and people often struggle to understand that a few degrees in temperature can make a big difference, but they can,” Forister said. “We are seeing these climate change impacts even in nice, natural areas and my feeling is that areas damaged by agriculture or urbanization are already lost to the butterflies.”

Forister said while temperatures will continue to rise, people can provide butterflies with some breathing room by conserving areas rife with wildflowers and cutting back on certain chemicals.

“The declines are extremely concerning ecologically, said Dara Satterfield, a butterfly researcher at the Smithsonian Conservation Biology Institute, who was not involved in the study. “We know butterflies and moths act as pollinators, decomposers, nutrient-transport vessels, and food sources for birds and other wildlife.

“This study is consistent with other large datasets from around the world, showing us that recent decades have presented new hurdles to survival for numerous butterfly species.”

This article was first published by The Guardian on 4 March 2021. Lead Image: A monarch butterfly balances on a flower in Vista, California. The number of western monarch butterflies wintering along the California coast has plummeted to a record low. Photograph: Gregory Bull/AP.

What you can do

Support ‘Fighting for Wildlife’ by donating as little as $1 – It only takes a minute. Thank you.




Fighting for Wildlife supports approved wildlife conservation organizations, which spend at least 80 percent of the money they raise on actual fieldwork, rather than administration and fundraising. When making a donation you can designate for which type of initiative it should be used – wildlife, oceans, forests or climate.


Dive in!

Discover hidden wildlife with our FREE newsletters

We promise we’ll never spam! Read our Privacy Policy for more info


Founder and Executive Editor

Share this post with your friends

Leave a Reply

Notify of