MONARCH BUTTERFLY

HABITAT North America, Hawaii, Portugal, Spain, Australia, New Zealand, and elsewhere in Oceania

THREAT Habitat loss

Like most butterflies, monarchs are highly sensitive to weather and climate. The species’ famous 3,000-mile migration from Canada to their winter home in Mexico is a trip made in search of optimal conditions: They need temperatures between 55 F and the low 70s along the route, and rain while they hibernate; an ideal body temperature is also crucial for mating, fertility, and egg-laying, which they must do where their caterpillars’ only food source, milkweed, is abundant. But storms and extreme temperatures are disrupting the monarchs’ routines. Once a summertime fixture, dappling backyard gardens from coast to coast, these crucial pollinators are disappearing. “They’re experiencing freezes in their winter

ing habitat, and drought and heat waves along their route,” Advani says. Higher temperatures may also be driving monarchs’ summer breeding grounds farther north, making their migrations longer and more difficult. One study recorded a 4.9 percent increase in their wing size over the past century and a half — an adaptation that likely arose to help them make the longer journey. Though monarchs aren’t endangered yet, their numbers are dropping. In 2018, there was a 15 percent decline in butterflies in Mexico compared to the previous year, and an 80 percent decline over the previous 20 years. One set of models predicts the population may drop so steeply in the next two decades, it won’t be able to recover.