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On her daily commute to the research facility, biologist Miriam San José crouches near a small water body covered by thick plants and retrieves a compact green audio recorder.

She had placed there overnight to record the characteristic calls of the Fowler's snouted treefrog, recognized by local researchers as an invasive species with effects that experts are just beginning to understand.

Despite teeming with remarkable animals – such as centuries-old large turtles, swimming iguanas, and the well-known finches that inspired Charles Darwin's evolutionary theory – the island chain near the shoreline of Ecuador had historically been free of amphibians.

During the 1990s, this shifted. Several small tree frogs made their way from mainland the mainland to the islands, likely as stowaways on cargo ships.

DNA studies indicate that, over the years, there have been multiple accidental introductions to the islands, and the frogs now have a strong presence on several islands: Isabela and Santa Cruz.

The population is growing so quickly that scientists have been struggling to monitor, calculating numbers in the hundreds of thousands on every island, across urban and farming areas, but also in the conservation natural reserve.

When San José marked frogs and attempted to recapture them in the following week and a half, she could find only a single marked frog from time to time, suggesting their populations were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very low," says San José. "I'm quite certain there are even more."

Deafening Noise and Rising Worries

The frogs' proliferation is clear from the acoustic chaos they cause. "The amount of frogs and the sound – it's really insane," comments San José.

For the researchers, their nightly vocalizations are helpful in determining their presence in remote areas, using recorders like the one outside San José's office.

But local farmers say the sounds are so raucous they prevent sleep at night.

"In the wet season, I constantly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a surprise, observing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about three years ago when one jumped on her palm as she was walking out of her house.

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, though. While the species has been in the islands for nearly three decades, scientists still know limited information about its effect on the archipelago's precariously balanced land and water ecosystems.

On archipelagos, it is very common for invasive species to thrive, as they have none of their enemies. The islands has over sixteen hundred invasive species, many of which are seriously affecting the safety of its endemic ones.

A 2020 study indicates the non-native frogs are voracious insect consumers, and might be disproportionately consuming rare bugs found only on the islands, or depleting the food sources of the islands' rare avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

The Galápagos frogs have shown some atypical characteristics, including surviving in brackish water, which is uncommon for amphibians.

Their development stage is also extremely variable, with some tadpoles turning into frogs very quickly and others taking a long time: the researcher witnessed one which stayed as a larva in her lab for six months.

"We truly don't know this aspect," she says, concerned the tadpoles could be impacting the region's clean water, a very limited resource in Galápagos.

Techniques to control the frogs in the early 2000s were mostly ineffective. Park rangers tried capturing significant quantities by hand and gradually increasing the salt content of lagoons in without success.

Research indicates applying coffee – which is extremely poisonous to amphibians – or using electrocution could help, but these approaches aren't always safe for other rare Galápagos organisms.

Without solutions to more of the fundamental questions about their lifestyle and impact, culling the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA techniques and genetic analysis will help her group understand of the invasive species, financial support for the research has been difficult to come by.

"Everybody wants to give funding for protecting frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."