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During her regular commute to the scientific station, biologist Miriam San José stoops near a shallow pond covered by thick vegetation and collects a small green audio device.

She had placed there through the night to capture the distinctive croaks of the Scinax quinquefasciatus, known by Galápagos researchers as an non-native species with effects that scientists are just beginning to comprehend.

Despite abounding with remarkable wildlife – including centuries-old large turtles, swimming lizards, and the well-known birds that inspired Darwin's evolutionary theory – the island chain near the coast of Ecuador had long remained free of amphibians.

During the 1990s, this shifted. Several tiny amphibians made their way from mainland Ecuador to the islands, probably as stowaways on cargo ships.

DNA research indicate that, through time, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a firm foothold on two locations: multiple locations.

The population is expanding so quickly that scientists have been struggling to keep track, estimating numbers in the millions on each island, across urban and agricultural areas, but also in the protected Galápagos national park.

When San José marked amphibians and attempted to find them in the subsequent 10 days, she could locate only a single tagged frog occasionally, suggesting their populations were enormous.

They calculated six thousand frogs in a single pond. "Our estimates are still very conservative," states San José. "I am pretty sure there are additional numbers."

Deafening Noise and Growing Concerns

The frogs' abundance is clear from the acoustic chaos they create. "The number of frogs and the noise – it's truly insane," says the scientist.

For the researchers, their nocturnal vocalizations are useful in determining their existence in remote areas, using audio devices like the one near San José's office.

But nearby farmers say the sounds are so raucous they keep them up at night.

"During the rainy period, I constantly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"At first it was a shock, seeing the first frogs in the area," says Larrea Saltos, 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 Unknown

The sound isn't the fundamental problem, though. While the amphibians has been in the islands for almost 30 years, experts still know very little about its effect on the archipelago's precariously balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for non-native organisms to thrive, as they have none of their enemies. The islands counts over sixteen hundred introduced species, many of which are significantly disrupting the survival of its native ones.

A 2020 study indicates the invasive amphibians are hungry bug consumers, and might be unevenly consuming uncommon bugs found only on the archipelago, or depleting the food sources of the islands' uncommon avian species, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their metamorphosis process is also highly variable, with some larvae becoming frogs very rapidly and others taking a extended period: San José observed one which remained as a tadpole in her lab for six months.

"We truly don't know this part," she says, worried the larvae could be impacting the islands' freshwater, a very scarce resource in Galápagos.

Techniques to curb the frogs in the beginning of the century were largely unsuccessful. Park rangers tried capturing large numbers by manual methods and slowly raising the salinity of ponds in without success.

Research suggests spraying coffee – which is extremely poisonous to frogs – or using electrocution could help, but these approaches aren't always safe for other rare 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 the biologist.

Financial Obstacles for Research

While she expects the increasing use of eDNA methods and DNA analysis will help her team understand of the invader, financial support for the project has been hard to come by.

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