All Queens Must Die On Santa Cruz Island, they killed the cows, sheep, and bees. Now it’s time to finish the job

By Ryan Bradley | Photography by John Francis Peters

The cows were the first to go because cows are big, and killing them was easy. The ranchers on Santa Cruz Island had been killing cattle for more than a century already. Rounded up, marched onto ships and motored 20 miles across the Pacific to mainland California, the cows were slaughtered, just like they’d been slaughtered for a hundred years, or longer even. By the early 1980s, the cows were gone. So were nearly all the ranchers. The National Park System is turning 100, and The Verge is celebrating with Wilderness Week: a look at the natural world, its freaky critters, and its future. The sheep were trickier. There were a lot more of them, something like 40,000, grazing over 96 square miles of mountainous island covered in dense chaparral, little oak woodlands, deep canyons, towering cliffs, and some of the largest sea caves in the world. A great landscape to hide in. The Nature Conservancy — which owns about three-quarters of the island — set about eradicating the sheep in 1981. By 1989, the Conservancy had killed at least 37,000 of them, but some sheep survived on Santa Cruz into the ‘90s. By 1997, the island began to open up, as part of the five-island Channel Islands National Park. The sheep carcasses dotting the landscape were not so great for public relations, and photos of wounded sheep and orphaned lambs made it into the papers and nightly news. The National Park Service paid to have the remaining sheep quickly rounded up and shipped across the channel. The program to remove the bees was far more tactically rigorous: for five years, beginning in 1988, scientists carefully mapped all the colonies, killing off the easy ones. In 1994, they introduced a parasitic mite to take care of the rest. By 2002, only one colony was left, on top of a grade named Matzana. Within seven months, that was gone, too. The snipers tracked the collared Judas pigs back to their kind The pigs were the trickiest. Or trickiest yet. They’d been on the island since the mid-19th century, brought over by the first ranchers, and had long gone feral. The Parks Service and Conservancy closed off most of the island to the public beginning in 2005, called in teams of New Zealand snipers and helicopter pilots and, within a year, had killed 5,000 of them. Over the next few months, some of the remaining pigs were captured and radio collared. Pigs are social, and extremely smart. The snipers tracked the collared, so-called Judas pigs back to their kind and, only if and when they could destroy a group all at once, opened fire. Any pig left alive, even wounded, would become all the more skittish and difficult to find. It would teach others to fear helicopters overhead. Some of the last remaining island pigs had changed their habits entirely. One Judas seemed to have turned amphibian. When a helicopter team flew by the patch of coastline where the radio collar told them it should be, they found a cave high up on a cliff. A harnessed sniper descended into the cave and, when the pig charged out of the dankness, he put it down. Santa Cruz Island was declared pig-free by 2007. In 2012, it was declared turkey-free, too. The Nature Conservancy was tantalizingly close to its goal — to restore Santa Cruz Island to something approximating its prehistoric, virgin state. There was but one invasive animal remaining, the toughest and hardiest creature of them all. For years, no one had figured out how to kill it. For half a century, no one even knew it was there. But it was, in the millions. And now the conservationists turned to face their most tenacious foe: the Argentine ant.

Imagine an ant: long delicate legs; a slim, dark, reddish-brown body; and antennae segmented 12 times. Its crawl or march or whatever you want to call it is distinctive — more of a scurry. And it isn’t alone. It’s surrounded by its sisters, a line of ants in front and behind, ready to swarm or attack or raid. They are relentless, these ants, which is why when you picture an ant — the type you go to war with every summer, summer after summer, in your kitchen and bathroom and backyard — the ant you are picturing is almost certainly Linepithema humile, the Argentine ant. The Argentine ant is one of the most successful invasive creatures on Earth. Their colonies appear on every continent but Antarctica, and many, many islands in between. They are so pervasive that the first of their species collected, named, and properly identified weren’t even in their native Paraná River drainage, which stretches across northern Argentina, Uruguay, Paraguay, and southern Brazil. No, the first Argentine ants were identified on Madeira, an island located a few hundred miles off the coast of Morocco, in the mid-19th century. Within a decade or two, they were spotted in Portugal, then Spain, Southern France, Italy, and the port of New Orleans. Trade globalized, and the Argentine ants colonized. They reached the Canary Islands and Azores by ship, and most of the southeastern United States and California by rail, likely carried in the dirt of potted plants. By 1902, Argentines were in Belfast, eking out the colder months in the warm walls of human homes. They can live pretty much anywhere, so long as there are humans and our climate-controlled structures. They have been found in greenhouses and inside zoos throughout the Midwest and into Canada. Southern California and the Mediterranean feel like home, though colonies have been found in apartments as far north as Sandnes, Norway. They wreak special havoc on islands, because most island ecosystems haven’t seen anything like them before. Hawaii had no native ants at all until trade and Europeans brought them. Argentines landed in the middle of the 20th century and ran rampant on Oahu and Maui. They’ve become the most dominant ant on Bermuda, too, pushing out a species of carpenter ant and so decimating the indigenous Bermuda ant that it was long thought extinct until, in 2002, an intern at the Bermuda Aquarium Museum and Zoo found a colony hiding inside an exhibit. The large supercolony, it turns out, is a global superpower Part of the Argentine ant’s success comes from its particularly relentless aggression. The Paraná River drainage is one of the more ant-choked regions in the world, and Argentines evolved to be the elbows out, bare-knuckle brawlers of the insect kingdom. Overseas, colonies spread freely through territories filled with weaker, ill-prepared ants, or no ants at all, and the Argentines rarely encounter a foe that can match them, save for other colonies of Argentines (or fire ants, another Paraná invasive). But another aspect of the species success overseas is its uniquely extended and frighteningly vast version of sisterhood: the supercolony. A colony of ants is a very large family of females. The genetic bond between certain colonies of Argentine ants is particularly strong. It’s so strong that a worker from one colony can be plucked up and deposited into another, hundreds of miles away, and she will act as if she’s right at home, surrounded by family, which, in a way, she is. Throughout California, from San Diego to San Francisco, the Argentine ants form one enormous sisterhood, or colony, or supercolony. The California supercolony is known in scientific literature as "the large supercolony." But recent studies suggest that it is even larger than it was long assumed to be. The lineage of the California colony is the same as colonies along the northern Mediterranean coastline and southern Japan. The large supercolony, it turns out, is a global superpower. Decades ago, it made landfall on Santa Cruz Island.

Christina Boser arrived on Santa Cruz fresh off her ecology dissertation and ready to help breed the island’s foxes, which had been on the brink of extinction. Instead, she got handed the list of invasive species to remove. The Argentine ants were all that remained animal-wise, though there were still plenty of invasive plants. "I’m an animal person," Boser told me. "So I got ants." That was seven years ago. She’s spent most of that time learning the ants’ ways and how to effectively poison them without harming other, noninvasive critters. The Nature Conservancy’s island eradication programs have always focused on benefiting an ecosystem as a whole, but it is particularly concerned with invasives that tip the ecological balance in such a way that it threatens native wildlife with outright extinction. Boser needed to poison all the queens at once Island eradications are always high-stakes, high-wire endeavors — you get, more or less, one big shot at taking out a whole species. Then you wait, sometimes years, to see if the invader has truly been eliminated or has, instead, come back. The coming back from the dead is called the Lazarus effect. Often all it takes is one pregnant female or a breeding pair to undo years of planning and millions of spent dollars. In the ants’ case, one stalwart queen stowed away underground could undo everything Boser had been plotting. Boser, extremely practical and one of those humans for whom the normal rules regarding reserves of energy and focus seem not to apply, had met an equally relentless foe. How do you eradicate tens of millions, if not billions, of tiny insects that live under several dozen square miles of extremely rugged terrain? Killing each ant would be an impossible task. But kill the queen and you initiate a colony collapse, for the queen is the only source of new ants. Only, Argentine ant colonies often boast several queens, so even the ant’s central weakness required a comprehensive plan of attack: Boser needed to poison all the queens at once. If she did that, Santa Cruz would be one step closer to perfection. "You’re looking at this landscape, you’re looking at millions of ants around one oak tree, and you’re thinking — how do you affect them all?" Boser said to me. "How do you get an ant to do what I want them to do?" She had Argentines in her backyard, of course, so she began her initial research and development there. Most poisoning systems acted too fast, killing ants either upon contact or soon after. Boser finally hit upon little gel beads, the kind used by florists in watery bouquets. Biodegradable, they soaked up the sugar water cut with poison, and kept their shape long enough, allowing the ants time to swarm and haul them homeward, back to the queens. Best of all, the sugar water bait balls took advantage of two quirks of the Argentine ants’ behavior. All ants live in a chemical world governed by pheromones. Argentines, in particular, are excellent at recruiting — telling other workers, via chemical scent, that there’s a valuable food source here, and getting many of their nest mates to follow. Those nest mates then lay more pheromones, and soon enough a swarm forms, be it around a dead cockroach, potato chip, or poisoned gel ball. The ants, craving carbohydrates, would swarm all over the poison. Particularly this time of year. Summer in California is Argentine ant season. It’s when they’re most on the march, hunting for food, invading kitchens and bathrooms. The ants are out of sync with the native flora and fauna of their adopted homes in coastal California, where nearly everything native has bloomed and died by July, if not earlier. The hills are dusty brown and gray and ready to burn. Most native ants, and many native insects, lie low or go dormant during the dog days. The Argentines, however, are roaming, hungry, and vulnerable. Boser moved her research from her backyard to a hillside near an old orchard on the island, not far from where the ants first made landfall sometime in the late 1950s or early 1960s. The ants had probably been carried to Santa Cruz by a Navy vessel hauling construction material, and soon colonized the wash and dry creek bed leading down to the small harbor. Decades passed, and the ants slowly worked their way up the wash, up into the orchard, then onto the hill beyond. But it wasn’t until 1996 when a biologist working in the old orchard reached up to a branch and came back down with Argentines scuttling all over his hand. "Oh shoot," he thought, "these aren’t supposed to be here." He added them to the list which, years later, was handed to Boser. After years of plotting and planning, Boser hoped to strike the indomitable ants a killing blow. Maybe. She wasn’t going to promise anything. "Ecology is really, really messy," she said. Then she invited me out to the island to see the mess.

Off the starboard bow on the twin-hulled double-decker ferry that shuttles back and forth from Ventura to Santa Cruz Island, a pod of common dolphins worked a school of fish, and children leaning over the railing screamed, delighted. An old ranch hand was telling me how he missed bow hunting the sheep; it had been good business, leading hunting parties. He’d worked on Santa Cruz for 45 years, but now that all the game was gone he mostly fixed the old rusted army trucks used by the scientists to bounce around from one study site to another. The old hand leaned back, tipped his cap down over his eyes, and dozed off for the rest of the three hour trip. Up ahead, through the marine haze, the outline of the island emerged. Its easternmost edge flattened out to a broad anchorage where the school kids and practically everyone else onboard would be let off. This was the National Park side of the island. Another five miles or so west along the coast we came to another anchorage, which led to a rocky, rough beach filled with sea detritus, and an even rougher wash leading into the island’s interior. At this landing, visitors need an escort, or a special permit, and are required to carefully wipe their shoes and check for stowaway species. This was The Nature Conservancy portion of the island. It was a fine-looking ant, I said. Probably the finest ant I’d ever seen Boser drove us up the wash toward the center of the island where we met David Holway, an ecologist from the University of California, San Diego, who specialized in ants — Argentines in particular. He was out in the field, searching for native ants in the shade of an old oak tree, and as he walked up to greet us he was distracted by a line of ants in the road. He squatted down and motioned us over. "These are harvester ants," he said. "Extremely rare." The ants crossed the road, carrying bits of grass into their nest. "That’s why they’re called harvesters," Holway said. "They’re bringing plant material back, dispersing seeds. They’re incredibly important to these ecosystems." There are 32 ant species on Santa Cruz, Holway said, though none were completely unique to the island. It's likely that several species ended up on the island after being blown across about 20 miles across the channel in the fall, when the Santa Ana winds blast offshore from California’s inland deserts, down the mountains, and out to sea. Many of the species on Santa Cruz were like these harvesters — nearly gone from mainland California, pushed out by Argentines, but still fairly common here. In a sense, the place had become a kind of ark for threatened native ants. We followed Holway to an island scrub oak: a shrunken-down, twisted-up variety unique to the Channel Islands. Another of the island’s endemics, a blue jay called the island scrub jay, featured short, stubby wings and was bad at flying. It made its home in these oaks, too. Holway beat at the dense, low-lying branches of the scrub with a special net, called a beating net, perfect for dislodging insects from the canopy. Bits of oak fell into the net, then a jumping spider, and then an ant. "Ah. Yes. Camponotus maritimus, a carpenter ant endemic to California. They’re gorgeous," Holway said. It was a fine-looking ant, I said. Probably the finest ant I’d ever seen. "Notice the two tones on the body," Holway said. "And the nice legs." "They’ve got great legs," Boser said. I nodded. Hours later, back at the old ranch where the Nature Conservancy ran its operations, a helicopter pilot and Boser went over the plan of attack for the gel pellet dispersal tomorrow morning. The system Boser has devised required two fork lifts, huge tubes filled with the gel pellets, a large metal chute, and the copter for dispersal. It was a complicated system, but it was the least complicated of the different systems Boser had devised. Plus, it hinged primarily on gravity to get the pellets from the chute into the bucket and gravity, Boser said, was more reliable than any machine. The next morning, on our way over to the landing strip and staging ground, we passed through huge strands of dried-up fennel, covering whole hillsides, and a grove of eucalyptus — both stubborn invaders like the Argentine ants. The fennel had spread considerably after the sheep were dispatched. They’d kept the plant in check. We passed by old pens where the island foxes had been bred when they were on the brink of extinction — an event caused by a complicated cocktail of invaders: golden eagles had been drawn to the island by piglets, which were easy prey, and welcomed as a check on the pig population. But then observers realized that the eagles were feasting on the native foxes too, and it was nearly too late to save them. In the endlessly intricate dance of keeping ecosystems balanced, the enemy of an enemy can turn friend then foe overnight. Approaching the old airfield, on the branch of a dying, dried-up oak, a prideful scrub jay hopped and flapped as if in hopes of scaring us off. Nearby, I began to see the mess of ecology and conservation in action. The first tub of beads had been poured into the chute, but was leaking out of a small gap at the chute’s end. Boser and a few others were staring up as a sticky mess of sugary beads fell into their faces. "Maybe some rubber, to jam up in there?" Boser said. The graduate students, in army surplus pilot jumpsuits, began shoveling the fallen beads, breaking the sugar water into a slurry and sending little droplets splattering. A ranch manager hopped down from his forklift and made quick work of an old hose, cutting bits of it to close in around the gap. With the gear patched, the helicopter pilot lifted off, tightly turning around and hovering with the bucket just under the chute, kicking up small bits of sugar water slurry before flying off down the coast, a few ridges over. As he made his first line, the tiny poison pellets shot out from the bucket, catching the sunlight and shimmering, diamond-like. By his fifth run, the patch had failed, and the gel bead slurry trickled out again. Boser sighed and walked back up toward the pellet tubs, near the small citrus grove where the ants were first discovered. The ants were still there, of course. For years she’d been tromping across these steep hills, dense with sage and mustard, running from wasps, looking for ant colonies, calculating the probability of their persistence even after mass aerial poisoning. If they fixed the chute, if the coverage was good, and if they did this again every month for another four months, for two full summers, she’d calculated that they had a very good chance of killing off the ants, close to 99.9 percent. Not perfect, but close enough.