Tucked between the two volcanoes that form Santiago Island, Puerto Egas was unlike any beach I had ever seen before. Layered rock formations rose up out of the black sand, creating stacked arches and tidal pools that attracted brightly colored Sally Lightfoot crabs, majestic marine iguanas, and playful sea lions. But something was keeping me from focusing on the natural wonder in front of me: wasps were buzzing incongruously around my head.

Unfortunately, the wasp incident was not an isolated episode. Even with my untrained eye, I saw the undeniable evidence of invasive species every single day I was in the Galapagos. Overwhelmed by their relentless presence, I wondered what it would take to rid these extraordinary islands of their menacing intruders.

Increased human travel to the Galapagos Islands since their discovery in the mid-1500s has introduced hundreds of alien species to the archipelago, both intentionally and accidentally. While many of these foreign species are harmless, some have spread throughout the islands like a disease, terrorizing native flora and fauna unprepared for the ecological onslaught. However, eradicating these pests is surprisingly complicated. So complicated, in fact, that I became convinced we may never again see a day when some of the most iconic native Galapagos species thrive on their own.

The primary reason that invasive species will never be eradicated from the Galapagos, I admit sheepishly, is that humans will inevitably inhabit the islands. While people are no longer directly threatening native Galapagos wildlife through hunting, their frequent shuttling to and from the mainland drastically increases the likelihood of foreign species introduction. The daily influx of cargo for the archipelago’s 30,000 residents and 150,000 annual visitors provides an easy conduit for seeds and critters to hitch a ride. And given the economic importance of the tourism industry, implementing strict quarantine regulations seems far too cumbersome to be plausible. The arrival of a new invasive species – or the return of an old one – remains a constant threat.

The ectoparasitic fly Philornis downsi is one such newly introduced species. Originally from Trinidad and Brazil, the fly was discovered on the Galapagos in 1997. The larvae, found in 64-100% of nests on 12 out of the 13 main islands, have been sucking the life out of newborn Galapagos finches, and scientists are just beginning to catch up to the problem. P. downsi’s accidental introduction is emblematic of how the Galapagos ecology is constantly changing, creating new challenges for conservationists at the drop of a hat.

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Once invasive species infiltrate the Galapagos, eliminating pests becomes its own complex challenge. An immediate barrier is money: when options for eradication are available, they are extremely expensive. Project Isabela, the elimination of feral goats on three of the islands, cost $10 million. Conservation requires continuous funding, which primarily comes from donor-dependent international organizations like the Galapagos Conservancy and Charles Darwin Foundation (CDF).

Even with unlimited cash, it seems impossible to eradicate certain intruders without also harming native species. Small but pervasive species, like rats, are extremely difficult to target without catching resident wildlife in the crossfire. In 2012, 22 tons of rat bait were dropped by helicopter on Pinzon island, blanketing 7 square miles with little blue poisonous cubes. Several organizations, including the Galapagos National Park and CDF, supported the move because the rats had been devouring the eggs of native giant tortoises and lava lizards. But the “raticide” sparked significant controversy, imperiling neighboring native species like the Galapagos hawks. While pesticides are often the best available option (biological interventions are technically challenging to develop), they cannot suppress invasive species without causing side effects.

The final piece of the puzzle, after thwarting new invasive species and removing existing ones, is actively helping endemic species recover. Some local fauna, like the tortoise and the mangrove finch, have been so decimated that they may be destined for extinction without significant help. On the other hand, Giant Tortoise rehabilitation is one example of seemingly productive human intervention. When tortoise populations had dwindled from thousands to dozens on some islands in the 1960s, they were taken in by humans and bred in captivity. Repatriation projects on Santa Cruz, Isabela, and Espanola have increased total tortoise populations to 26,000, but the current dependence on human assistance sparks questions about whether the intervention itself is unnatural, or unsustainable. Although the repatriated tortoises have begun to mate by themselves in the wild, it is unclear if they can maintain their numbers once captive breeding stops. After all, many foreign enemies of the tortoise, like cats and fire ants, still roam free.

Conservationists in the Galapagos need to execute a three pronged attack to win the biological battle against invasive species – they must remove existing invasive species, prevent new aliens from coming in, and help endemic species recover. Although conservationists have helped keep 95% of the original Galapagos species alive, their work is far from over; in fact, it may never be over. Ridding the Galapagos of its pests is not a one-time challenge, like curing small pox; rather, it is a constant battle that requires disciplined adherence to a complicated plan. As long as humans live on the islands, people will have to continually fight to reverse the damage caused by their own species in order to protect the beautiful endemic wildlife of the Galapagos.

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Laura Santoso is a student at the California Institute of Technology. This article is the result of a research project undertaken during the Winter 2014 Evolution course.