Butterflies in the Storm

Battling rising seas and creeping asphalt, scientists race to save two endangered species.

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.

Once common throughout much of coastal Florida, the sapphire-colored, quarter-sized Miami blue is now among the world’s rarest butterflies. Records show that it once ranged from St. Petersburg to Cape Canaveral and throughout the Keys. But scientists, including Jaret Daniels, an entomologist at the Florida Museum of Natural History and the University of Florida who has studied the butterfly for more than two decades, recognize that these accounts may be incomplete. The Miami blue was so ordinary, he said, that collectors eager to capture unusual species simply ignored it.

The Miami blue’s range began contracting southward in the 1970s, like a fast moving tide. The overriding cause of the butterfly’s decline remains uncertain, but it coincides with the spread of canals, condos, beach houses, and retirement communities along the south Florida coast. The butterfly’s preferred habitat—sandy low-lying beach berms—is also coveted by oceanfront developers. Other factors, including pesticides and invasive species, may have caused small, isolated populations to become more susceptible to disruptions like storms. After Hurricane Andrew hit Florida in 1992, Miami blues seemed to be no more.

For the next seven years, not a single one was spotted. The once-common butterfly was presumed extinct. Then, unexpectedly, a butterfly enthusiast discovered a handful in Bahia Honda State Park in the Florida Keys in 1999. But they too were gone by 2010, after an unusually cold winter took its toll, and an invasive green iguana ate up the butterfly’s host plant, a thorny bush called gray nickerbean (Caesalpinia bonduc). Officials removed nearly 600 iguanas, but the Miami blue never came back. In the meantime, though, Miami blue butterflies showed up 50 miles west, on a handful of low-lying uninhabited islands in the Florida Keys National Wildlife Refuge.

In 2017, as Hurricane Irma approached the Keys, the storm shifted east, veering away from the refuge. Instead, the hurricane’s full force struck at Cudjoe Key, not far from Bahia Honda, where Sarah Steele Cabrera, a researcher at the Florida Museum of Natural History who works with Daniels, was preparing to release hundreds of captive-raised Miami blue larvae onto newly planted gray nickerbean. Winds peaked at 130 miles per hour, clawed at roofs and trailer siding, toppled trees, and downed power lines. More than a month’s worth of rain fell in less than 72 hours and the storm surge swept saltwater miles inland, drowning neighborhoods and slopping seaweed and mud onto the plates in Steele Cabrera’s kitchen cupboards.

Six months later, on a warm sunny day in early March, Henry and Steele Cabrera nosed a skiff and a Zodiac toward the sandy shore of Boca Grande Key, one of the islands in the Key West National Wildlife Refuge, about 15 miles west of Key West. They were making the trip, along with Haddad and Martha Burford Reiskind, an applied ecologist from North Carolina State University, to see how this population of Miami blue butterflies—and their beachfront habitat—had weathered the storm.

On shore, butterflies swirled above the coastal prairie grasses next to the desiccated skeletons of violently uprooted shrubs. Crab traps and buoys lay abandoned on the beach. Several yards inland, Miami blue butterflies bounced on the air above a dense thicket of Florida Keys blackbead (Pithecellobium keyense)—a wide bush with fat, stiff, teardrop-shaped leaves. Nearby, they sipped nectar from the small white flowers of a mint-like plant called snow squarestem (Melanthera nivea). “There are so many!” Haddad said with gusto. Depending on the species, rare butterfly researchers may hardly ever see their subjects, but there were perhaps a dozen Miami blues close by. “I remember my first trip out here, thinking, there are so many, how can there be a problem?”

Due to their scarcity throughout most of their historical range, Miami blue numbers are hard to pin down. From egg to butterfly old age, their life cycle lasts about a month, and their numbers can see huge swings. When biologists first stumbled upon the Miami blues here on Boca Grande and in the nearby Marquesas Keys in 2007, shortly after Hurricane Wilma, they reported seeing swarms of 400 to 500. But during later visits by Daniels and others, their numbers barely cracked double digits.

If there was a boom-bust cycle at play, its cause wasn’t clear. When Henry began studying the Miami blues a few years later, she was equally perplexed. At first she thought their abundance was tied to the time of year, but that proved wrong. Then she hit upon rainfall. A month of good rain sparked new growth on the blackbead—caterpillar food—and 30 days later, pop!, a kaleidoscope of Miami blues would rise in to the air.

It had now been six months since Irma, and in the lead-up to this spring’s visit rainfall had been scarce. After the wettest rainy season in 86 years, South Florida had seen several months of unusually hot, dry weather. The conditions didn’t bode well for the Miami blue. “This is all so crispy,” said Henry, surveying the blackbead. She had pulled the Buff she wore around her neck up to her eyes to block the scorching sun. “These are old waxy leaves that are probably less palatable to caterpillars,” she said grasping a branch of the blackbead. “The new ones are brighter green and fleshier, they’re more like spinach, and less like—this doesn’t look tasty to me—weathered cabbage.”

Steele Cabrera stooped over the blackbead, grasped a stem, and flipped it over. She was looking for eggs and caterpillars—and also for ants. The ants feed off a sugary substance produced by Miami blue larvae and, in return, chase off predators and parasites, such as wasps. She found ants, peered closer, and pointed to a white, pinhead-sized fresh egg. There were others, too, including some that had hatched. But no caterpillars.

Steele Cabrera and Henry trudged through the sand counting butterflies to estimate their population size. Much of the blackbead had been swallowed by the ocean as the beach had eroded. In some places, almost 60 feet of beach had been lost in only a few years. Henry had expected some of the change, part of the ocean’s give and take to shape and re-shape these sand islands, but not this much.

Climate change was becoming an increasingly important factor here. The sea level rise projections are not rosy for the Keys. Sea-level gauges, including one in Key West that has been there for more than 100 years, document the rising water. Between 1913 and 2017, sea levels rose by about 24 centimeters (9.5 inches) here. According to the U.S. Army Corps of Engineers, sea levels in south Florida will rise another 7.5 to 18 centimeters (3 to 7 inches) by 2030. Boca Grande lies only 3 feet above sea level. Irma had only side-swiped these islands, instead of barreling through them, and Henry had hoped the storm might have benefitted the butterflies, by replenishing the coastal meadows with sand for small flowering plants, in addition to bringing rain and encouraging new blackbead growth. But now she was unsure: They weren’t extinct, but they weren’t thriving either.

Haddad, who was also counting Miami blues, crashed out of a nearby thicket. “I think Miami blues are screwed on Boca Grande,” he said. Ordinarily, Haddad is surprisingly optimistic for an ecologist who studies species on the brink. He tends to see challenges as opportunities, failures as signs to look elsewhere for success. While playing pickup basketball in 2014, Haddad fell, cracked his head, and suffered a traumatic brain injury that left him with a two-month hole in his memory and many months of recovery ahead of him. He has almost fully bounced back from the near-death experience, and he is thankful that he has an opportunity to think about how to restore rare butterflies. But now he sounded uncharacteristically grim. “In a decade or two, maybe sooner, with sea level rise—they’re gone,” he said.

Which is not to say that Haddad had lost hope altogether. “What I am optimistic about here is that new habitat can be restored on more accessible keys,” he said. Access was important for the researchers, who could only get to Boca Grande and the Marquesas Keys on calm days. But he also wondered about the public, which was restricted from accessing the vegetated areas where the Miami blue lived on those beaches. “If nobody can see it, then who values it?” said Haddad. “We don’t want this to go extinct, but it is so ethereal, it means nothing if you can’t see it, if nobody can see it.”

Bahia Honda State Park was one of those areas where the public might one day camp and picnic among the Miami blues. Later in the day, after a bumpy boat ride back to Key West and an hour-long drive east along the one-lane Overseas Highway, the ecologists slipped through a padlocked chain-link fence to visit the eastern edge of the park, closed off since Hurricane Irma. In 2017, Steele Cabrera had planted hundreds of grey nickerbean seeds and seedlings along the park’s beaches in anticipation of reintroducing the butterfly to the wild that fall.

Irma had postponed those plans, cancelling the release of the captive-bred larvae—and the park was not yet fully restored. As they walked along the wide beach, they could now see where the storm had ripped up the parking lot and swept acres of new sand onto it. Yet many of the plants had survived. The small white flowers of scorpion-tailed heliotrope and Spanish needles flourished. “The Miami blues will do well here, because they have so much nectar,” said Steele Cabrera. Hundreds of caterpillars would soon be chauffeured to the Keys from Daniels’ lab in Gainesville, and it would be reintroduced in July. Resurrecting the Miami blue seemed doable: The butterfly could be lab-bred and raised, and there was still plenty of sandy beach available for scientists to plant thorny grey nickerbean and blackbead.

For the Bartram’s scrub hairstreak, the other butterfly under Henry’s supervision, the path forward is not as clear. The butterfly, whose wings are streaked charcoal and white with a daub of rusty orange, was never as widespread as the Miami blue. Nor does much of its habitat remain. The Bartram’s depends on pineland croton (Croton linearis), a rare plant that grows only in pine rocklands—an ecosystem underpinned by limestone and filled with slash pines, saw palmettos, poisonwood and a lush, herbaceous understory that once covered nearly 200 square miles of south Florida. Fire had historically kept the understory open and available for croton to grow.

More than 90 percent of Florida pine rockland has been cleared for development over the past century. Outside of Everglades National Park, only two percent of pine rockland remains in the U.S., with the largest chunks in Miami-Dade county and on Big Pine Key. Many of the remaining pine rockland fragments abut shopping malls, homes, and roads, presenting a problem for ecologists who might like to rekindle the fires that once kept this ecosystem in balance. One 136-acre sized chunk of pine rockland, once part of an Army blimp base, sat neglected for years near the Miami Zoo. Today, it is slated for development of a site that will include a Walmart, LA Fitness, and 900 condos.

Early one morning, Henry led the group on foot along a hardscrabble road near the center of Everglades National Park and then plunged into the dry savannah. She wove among charcoal-black trunks and ankle-breaking holes, scanning the understory for the orange flagging tape she had used to mark the spindly, rosemary-like croton plants. Henry gently turned back the long slender leaves, looking for signs of butterflies. Bartram’s eggs seem invisible to the untrained eye, and the tiny, croton-colored caterpillars are not much easier to spot. But they grow fast, about a millimeter each day into two-centimeter-long “croton sausages,” said Henry. “Monster!” she yelped when she spotted one. It was a beast: 13.6 millimeters. “I get excited when they get this big and I think they’re going to make it.”

The National Park Service had burned this block of pine rockland in June 2017, for the first time in a decade, to prevent the imperiled ecosystem from giving way to hardwood forest. It was also the spot with the highest survival rates for Bartram’s that year, prior to burning. The Service aims to set fire to the pine rockland every three years. “The plan is to never burn adjacent blocks, so that the butterflies over there can recolonize this block here,” said Henry, pointing across the road. Henry now builds screened enclosures around the plants that are hosting large caterpillars ready to pupate, and removes the screens once the butterflies emerge, so she can know their fate.

Two days later, on Big Pine Key, Henry pulled off to the side of a quiet road near a scrappy tract of pine rockland. Irma had made landfall not 10 miles from here, and the debris remained piled up. Watermelon-sized lumps of concrete lay beside twisted vines of rusted rebar and puddles of beach sand. Leafless mangroves and buttonwoods edged the road, festooned with seagrass tinsel, bait freezers, and plastic deck chairs. The 5,000 people who live and work on Big Pine Key were still piecing together their lives, some living in damaged homes covered with blue tarps and others in tents in their yards.

Slash pines, with their wide but shallow root systems, lay sprawled, knocked out by the hurricane’s force. Others had snapped. The forest floor was thick with leaves, boughs and trunks. Here and there, in open areas, scrawny croton plants poked out of thick carpets of dried grasses. It had been more than a year since a Bartram’s had been seen here, but recently nibbled croton leaves gave away the butterfly’s presence. “There should be a caterpillar in here,” said Henry. Throwing her sunglasses aside, she knelt on the ground, poking through grass and sticks, and lifting rocks. “These are all the signs of a big caterpillar. Bartram’s are not extinct out here.”

Some of the best Bartram’s habitat on Big Pine Key lies just behind the local shopping mall. It’s an area where people coping with homelessness set up camps. Occasionally, their campfires spill over, clear the brush and accidentally restore a small piece of the pine rockland. But talk of prescribed burns near populated centers is still met with resistance, although attitudes are shifting, said Haddad. “What we once viewed as harmful are actually natural parts of ecosystems, and we need them. We just need to strike the right balance,” he said.

Or they need to find alternatives. In 2015, Henry set up an experiment on a stretch of pine rockland. She wanted to see if a human-made, mechanical disturbance could offer the Bartram’s the same benefit as fire. She hired a skid steer equipped with a masticating head to drive haphazardly through her experimental plots. “It looked bad. The public was not thrilled,” she said. But by 2017, the results looked promising. In the mechanically cleared plots, the croton was just as likely to survive as in untouched plots, and new plants were far more likely to sprout. It wasn’t as successful as in the burned areas in the Everglades, “but it’s better than doing nothing,” Henry said.

Then Irma rolled through, and Henry had to rethink her plan: Would the hurricane clear spaces in the understory and help the croton grow and survive? Later in March, Henry and Steele Cabrera returned to their sites across the island to look for the nearly 600 croton plants they’d previously marked and numbered with shiny silver tags. But they didn’t find wide open spaces. Instead they found plants buried under overturned pine trees, branches, and palm fronds that had been swept to the ground by the hurricane. Some of the plots were under a foot of debris, and others they could barely mark out. “Some of my big healthy plants at the south end of the island are all skeletons now,” said Henry. In all, 70 percent of the croton were now dead. “What optimism I had is gone.”

Scientists from both sides of the Atlantic are reporting huge declines in butterfly populations—as much as 75 percent in some cases. Insects overall are under threat, with some researchers calling it the “Insectegeddon.” Yet despite the global gloom—and frequent local setbacks—the ecologists watching over Florida’s rare butterflies cling to an undercurrent of hope.

They’ve seen the large blue butterfly restored to the U.K. They’re seeing growing numbers of the St. Francis’ satyr in North Carolina, following the careful rescue of a wetland from choking shrubby vegetation. They’ve figured out some of the factors that help keep the Miami blue alive and have successfully raised generations upon generations of them in the lab. Bringing back natural disturbance can give rare butterflies the open spaces they can’t do without. Now, if Henry and others can figure out a way to restore the natural habitat of the pine rockland, they may well be able to give the Bartram’s scrub hairstreak a suitable place to live as well.

A month later, in late April, a large brush fire broke out on Big Pine Key. The fire moved fast, through years of dry understory growth and post-hurricane brush. It burned one home and 100 acres of pine rockland, including an area that Henry had labeled as Bartram’s “occupied habitat.” But Henry was cautiously upbeat. Perhaps the fire would open up the pine rockland and give the croton—and the Bartram’s—space to grow. It might also change the conversation about prescribed fires on the island, she said. Years of fire suppression can lead to catastrophic fires that burn hot and out of control, threatening homes and other infrastructure. Small, more frequent, controlled fires can help offset that threat. “I think it’s potentially good for butterflies in the longer term.”

Hannah Hoag

Hannah Hoag is an award-winning freelance journalist and editor based in Toronto, Canada. She has published stories in Nature, The Atlantic, Discover, Wired, New Scientist, Sapiens, The Globe and Mail, and elsewhere. She is the former (and founding) editor of Arctic Deeply and a contributor to The Science Writers’ Handbook.

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