As Hurricane Irma was bearing down on the Florida Keys last September, Erica Henry was watching from Raleigh, North Carolina. Henry, an ecologist, had packed up and left the Keys at the start of hurricane season and was supposed to be working on her doctoral thesis. But instead of writing code for a butterfly population model, she was checking and re-checking the hurricane’s projected path and posting anxious updates to Twitter.
For six years, Henry had been studying some of the rarest endangered butterflies in North America, and she feared the storm seething through the Atlantic might gobble them up for good. “We always talk about how one hurricane could be the end of them,” said Henry. The day Irma slammed into the Keys, Henry approached one of the members of her advisory committee with a question: “What happens if one of your study species goes extinct during your dissertation?”
Of the 25 native butterflies on the U.S. endangered species list, four reside in Florida. Henry is studying two of them, the Miami blue (Cyclargus thomasi bethunebakeri) and Bartram’s scrub hairstreak (Strymon acis bartrami). A former ski bum who wearied of waiting tables, Henry now copes with south Florida’s blistering sun, thorny bushes, and infinite mosquitoes in an effort to grasp what helps these butterflies thrive—and what might stave off their demise.
For decades, efforts to save the world’s rarest butterflies have come up short. Many species have only become rarer—or extinct—sometimes after scientists and conservationists adopted seemingly cautious interventions that turned dire. Nick Haddad, Henry’s supervisor, likes to tell a story about the large blue butterfly (Maculinea arion eutyphron). First recorded in 1795, it became extinct in the British Isles in 1979.
More than a hundred years ago, conservationists erected fences around fields that housed the disappearing butterfly to keep out both butterfly hunters and cattle. But it turned out grazers were key to the butterfly’s survival, keeping grasses short so that ants could squirrel the caterpillars below ground for 10 months until the butterflies emerged. (Butterfly larvae look remarkably like ant larvae, so the ants carry them into their nests where the butterfly larvae feast on developing ants.) Over time, the fields became overgrown, the soil temperature dropped, and other ant species with no interest in the large blue moved in.
Fencing off the fields “was exactly the wrong thing to do,” said Haddad, an ecologist at Michigan State University who studies wildlife corridors, butterflies, and bees. “The very acts of conservation were dooming butterflies.” Another large blue subspecies from Sweden has since been introduced in the UK—and cattle munching on grasses have contributed to their success.
Now, after watching endangered butterfly populations dwindle and sometimes wink out, butterfly ecologists are finally getting a handle on what it takes to give a rare butterfly a leg up. Farming, urbanization, and forestry have carved up habitat, wiped out key plant species, and squelched natural disturbances like fire, flooding, and grazing, that help keep butterflies alive. And when isolated fragments of rare habitat sit adjacent to homes or schools—or on the edge of rapidly rising seas—the extinction risk only grows. Ecologists have discovered that by re-introducing this natural disturbance, often in combination with captive breeding programs, they can set butterflies on track to recovery.
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