Butterflies arguably belong to summer, but the summers we’re having now are starting to work against them. 

Butterfly populations across the United States have dropped 22% over 20 years, and extreme heat is one of the reasons why.  Two-thirds of the more than 550 species studied declined by more than 10%.

Butterflies are cold-blooded, so they thrive when temperatures are between 75 and 84 degrees Fahrenheit. When it gets above 91, their metabolism, immune systems and reproductive capacity all start to break down.

(MORE: Heat index and the danger of high temperatures)

Conservationists in Pakistan have observed that during extreme summer temperatures, the lifecycle of butterflies is slashed by nearly half – reduced to 15 to 20 days.

"The butterflies are an important component of biodiversity, and they are the biological indicator of a healthy ecosystem. The same way as humans are affected by the heat waves, these tiny winged creatures are also affected by the heat waves," says Bushra Nisar Khan, assistant professor of zoology at the University of Punjab.

In North America, the population of one of the most well-known butterfly species, the monarch, has declined by more than 80%. In 2024, the U.S. Fish and Wildlife Service proposed listing it as a threatened species under the Endangered Species Act.

While habitat loss and the use of insecticides are also to blame for the decline of butterflies, researchers have found heat plays a major role. Within the U.S., one study found stronger declines in southern regions where temperatures are rising faster. It also noted that the two regions with the most negative declining trends — the Southwest and the Mountain-Prairie regions are also home to eight of the 10 driest U.S. states.

(MORE: Heat is America's deadliest weather)

What you can do

As the world experiences more frequent heat waves, anyone and everyone can help by creating a sanctuary for butterflies right in your own backyard.

• Plant native, butterfly-friendly flowers. You can find out which pollinator plants are best for your region by searching lists on the websites of groups like the Xerces Society for Invertebrate Conservation or the National Wildlife Federation. 
• Add a puddle. A shallow dish of wet sand or pebbles gives butterflies the moisture and minerals they need to survive hot days.
• Skip the pesticides and insecticides. Insecticides have been identified as leading causes of butterfly declines in recent analyses in the midwestern US and California.
• Join a citizen-science butterfly count. The International Monarch Monitoring Blitz runs July 31 through August 9 — anyone in North America can photograph monarchs and upload them.

Butterflies have helped make summer look magical for generations. Whether they still do a decade from now depends less on any one warm July than on what we do the other 11 months of the year.