Beginning in the 1900s, U.S. hunters imported Eurasian wild boar for sport; today’s feral swine threaten firefly larvae and turtle nests across the Southeast

Each spring, thousands of visitors drive into Congaree National Park in South Carolina to watch fireflies flash in unison after dark. It is among nature's most unusual light displays, but a National Park Service report says that show is threatened by an unlikely source: wild pigs. Park superintendent Greg Hauburger said the animals dig up firefly larvae before they can glow, along with turtle eggs, ground-nesting birds and rare native plants. NPS reporting on the broader threat notes feral swine are causing similar damage in more than 40 parks across the Southeast.

A hunting hobby that backfired

Feral pigs aren't new to America. When explorers and settlers came over in the 1500s, they brought domestic pigs with them as a food source. Many escaped or were released. Centuries later, starting in the 1900s, hunters imported Eurasian, or Russian, wild boar for sport. Escaped farm pigs and wild boars interbred over time. The result: today's feral swine, a tough, adaptable hybrid that can survive almost anywhere, and that adaptability is the problem. These pigs reproduce quickly, eat just about anything, and have few natural predators in the United States. The National Park Service reports that feral swine have now been spotted in at least 35 states. The U.S. Department of Agriculture fact sheet notes that the nation's feral swine population is believed to be more than 6 million, and that feral swine are a contributing factor in the decline of nearly 300 native plant and animal species, over 250 of which are already listed as threatened or endangered.

Why Congaree's fireflies are going dark

Fireflies do not glow throughout their entire lives. According to the Xerces Society, a leading nonprofit for insect conservation, for one to three years, they are larvae, buried in moist soil and leaf litter, hunting snails and worms below ground, before they emerge as the flickering insects most people know. This is a sensitive stage. The Xerces Society says firefly larvae are especially vulnerable to disturbed soil because it destroys the moist, undisturbed ground layer they need to survive and grow. That's exactly the type of damage feral swine do. Pigs "root," meaning they use their snouts to dig up dirt, as they look for food. A single sounder, or herd of pigs, can damage large areas of forest floor. This rooting threatens the larvae just below the surface at Congaree and could disrupt the park's synchronous firefly season.

Turtle nests don't stand much of a chance either

Feral swine cause damage above and below ground. They’ve become one of the biggest threats to nesting sea turtles along the southeastern coast. The 2019 study, ‘Feral swine harming insular sea turtle reproduction: The origin, impacts, behavior and elimination of an invasive species,’ published in the journal Acta Oecologica tracked feral swine at North Island, South Carolina, and found that once the animals located the nesting beach, they caused nearly total losses of sea turtle nests there in 2010 and 2011, back-to-back seasons Researchers estimate that the cumulative loss from destroyed nests was as high as $1.16 million between 2010 and 2016.

Park biologists say the pattern is similar elsewhere. Feral swine were responsible for finding, rooting up, and eating the eggs of more than 90 percent of nests at one southeastern park in the 1990s, according to National Park Service natural resources manager Kelly Irick. When a pig finds a nest, it typically keeps coming back to that area of the beach until all the nests in the neighborhood are gone.

Fighting back, one hog at a time

The good news is that removal efforts can work. Wildlife biologist Doug Hoffman told local reporters that when he began working on the problem at Cumberland Island National Seashore, the population stood at 500 to 600 hogs; it's now fewer than 200. Since then, sea turtle nesting has recovered substantially along the island's 18-mile beach, with NPS recording a record 1,248 loggerhead nests in the 2022 season alone. Great Smoky Mountains National Park wildlife managers have eliminated almost 15,000 feral swine through trapping, targeted shooting, and public hunting since control efforts began in 1959, according to the National Park Service.

Thanks to funding from the Inflation Reduction Act and the Bipartisan Infrastructure Law, according to NPS, more southeastern parks are expanding these programs. Carrie Allison, a wildlife biologist for the National Park Service's Southeast Region, said the funding gives parks the resources to reduce pig numbers and maintain those reductions, which is good for park land and the private land around it.

Why this should matter to you

Fireflies and sea turtles are the kinds of wildlife most people associate with summer memories, whether that is a night hike or a beach trip. Their loss has real consequences for visitors and ecosystems. Feral swine control seldom makes the headlines outside of conservation circles. Whether the next generation sees synchronized fireflies or hatching sea turtles in person, rather than in old photographs, is a question the National Park Service is quietly addressing.