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On her daily commute to the scientific station, biologist Miriam San José stoops near a shallow water body surrounded by thick plants and collects a small plastic audio device.

The device was left there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local researchers as an non-native species with consequences that experts are starting to comprehend.

Despite teeming with remarkable animals – including ancient giant tortoises, marine lizards, and the famous finches that inspired Charles Darwin's theory of evolution – the Galápagos archipelago off the shoreline of South America had historically been devoid of amphibians.

During the 1990s, this changed. Several tiny amphibians traveled from mainland Ecuador to the islands, probably as stowaways on cargo ships.

Genetic research suggest that, through time, there have been multiple accidental arrivals to the islands, and the amphibians now have a strong foothold on several islands: multiple locations.

The population is expanding so rapidly that scientists have been struggling to monitor, estimating populations in the millions on each island, across urban and agricultural areas, but also in the protected natural reserve.

When San José marked amphibians and attempted to recapture them in the subsequent week and a half, she could find only a single tagged frog occasionally, indicating their populations were enormous.

They estimated six thousand frogs in a single pond. "The calculations are still very low," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is evident from the acoustic disruption they cause. "The number of frogs and the sound – it's truly incredible," says San José.

For the researchers, their nightly mating calls are useful in estimating their presence in far-flung areas, using recorders like the one near the office.

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

"During the rainy period, I constantly hear their croaks 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 the farmer, who started noticing their large numbers about several years ago when one jumped on her hand as she was walking out of her front door.

Ecological Impact Stays Unclear

The sound isn't the fundamental problem, though. While the amphibians 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 islands, it is very typical for invasive organisms to prosper, as they have none of their enemies. The islands counts 1,645 invasive types, many of which are significantly disrupting the survival of its native ones.

A recent study suggests the invasive frogs are hungry bug eaters, and might be unevenly eating rare insects found exclusively on the archipelago, or reducing the food sources of the region's uncommon avian species, affecting the food chain.

Unusual Traits and Control Challenges

The island amphibians have exhibited some atypical characteristics, including surviving in brackish water, which is uncommon for amphibians.

Their development process is also highly variable, with some tadpoles turning into frogs very rapidly and others taking a long time: San José witnessed one which stayed as a tadpole in her laboratory for six months.

"We truly don't know this part," she says, worried the larvae could be affecting the region's clean water, a very limited resource in the islands.

Techniques to control the amphibians in the beginning of the century were mostly ineffective. Conservation officers tried capturing large numbers by manual methods and gradually increasing the salt content of lagoons in without success.

Studies suggests spraying caffeine – which is extremely toxic to frogs – or using electrocution could assist, but these methods aren't necessarily secure for other uncommon island organisms.

Without solutions to more of the fundamental issues about their lifestyle and effect, culling the frogs might not even be the right way to proceed, says San José.

Financial Obstacles for Study

While she expects the increasing use of eDNA methods and DNA analysis will help her team understand of the invasive species, funding for the research has been hard to come by.

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