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On her daily walk to the research facility, biologist Miriam San José stoops near a shallow pond covered by thick plants and retrieves a compact plastic audio device.

The device was left there overnight to capture the distinctive calls of the Scinax quinquefasciatus, known by local researchers as an non-native threat with consequences that scientists are starting to comprehend.

Although abounding with unique wildlife – such as ancient giant tortoises, marine lizards, and the famous birds that sparked Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had long remained free of frogs and toads.

During the 1990s, this changed. Some small amphibians traveled from continental Ecuador to the archipelago, likely as hitchhikers on cargo ships.

DNA research suggest that, through time, there have been repeated unintentional arrivals to the islands, and the frogs now have a firm foothold on two locations: Isabela and Santa Cruz.

The numbers is expanding so rapidly that researchers have been finding it difficult to monitor, estimating numbers in the millions on every island, across urban and farming areas, but also in the protected natural reserve.

When the biologist tagged frogs and attempted to find them in the following week and a half, she could locate only a single tagged frog from time to time, indicating their populations were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states the researcher. "I am pretty sure there are even more."

Deafening Noise and Rising Worries

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

For the researchers, their nightly mating calls are useful in determining their existence in remote areas, using audio devices like the one outside San José's office.

But nearby farmers say the sounds are so loud they prevent sleep at night.

"During the rainy period, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"Initially it was a surprise, observing the initial frogs in the area," says the farmer, who started noticing their abundance about several years ago when one jumped on her palm as she was walking out of her house.

Environmental Consequences Remains Unclear

The noise isn't the primary problem, though. While the species has been in the Galápagos for almost 30 years, scientists still know very little about its impact on the islands' precariously balanced land and water environments.

On archipelagos, it is very typical for invasive organisms to thrive, as they have few of their enemies. The Galápagos counts 1,645 invasive species, many of which are seriously affecting the survival of its endemic ones.

A recent study suggests the non-native frogs are hungry bug eaters, and might be disproportionately consuming rare bugs found only on the islands, or depleting the nutrition of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos frogs have shown some unusual traits, including surviving in brackish water, which is rare for frogs.

Their metamorphosis process is also extremely variable, with some tadpoles becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a tadpole in her laboratory for half a year.

"We really don't know this aspect," she says, worried the tadpoles could be impacting the region's clean water, a very scarce resource in the islands.

Methods to control the amphibians in the beginning of the century were mostly ineffective. Park rangers tried capturing large numbers by manual methods and gradually increasing the salinity of ponds in vain.

Research indicates spraying caffeine – which is extremely toxic to frogs – or using electrocution could assist, but these methods aren't always safe for other rare Galápagos species.

Lacking answers to more of the fundamental issues about their lifestyle and effect, culling the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she hopes the growing use of eDNA methods and DNA analysis will help her group understand of the invader, financial support for the project has been difficult to obtain.

"Everyone wants to give support for preserving frogs," says the researcher. "But it's harder to find financial backing for an introduced frog that you might want to control."