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During her daily commute to the scientific station, biologist Miriam San José stoops near a shallow pond surrounded by thick vegetation and retrieves a small plastic sound device.

She had placed there overnight to capture the characteristic calls of the Scinax quinquefasciatus, known by Galápagos researchers as an invasive species with effects that experts are starting to understand.

Despite abounding with remarkable wildlife – including ancient giant tortoises, swimming iguanas, and the well-known finches that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago off the coast of South America had historically been devoid of frogs and toads.

During the 1990s, this shifted. Some small amphibians made their way from continental the mainland to the archipelago, probably as hitchhikers on cargo ships.

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

The population is expanding so rapidly that researchers have been struggling to keep track, calculating populations in the millions on each island, across developed and farming areas, but also in the protected Galápagos national park.

When San José marked frogs and attempted to find them in the following 10 days, she could locate only a single marked frog from time to time, indicating their populations were enormous.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I am pretty sure there are even more."

Deafening Noise and Growing Concerns

The frogs' proliferation is clear from the sound disruption they create. "The number of frogs and the sound – it's truly incredible," comments San José.

For the scientists, their nocturnal vocalizations are helpful in estimating their presence in far-flung areas, using recorders like the one near San José's workplace.

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

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

"Initially it was a surprise, observing the first frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her palm as she was stepping out of her front door.

Ecological Impact Remains Unclear

The noise isn't the fundamental problem, however. While the species has been in the islands for nearly three decades, experts still know very little about its effect on the islands' delicately balanced terrestrial and aquatic environments.

On islands, it is very typical for non-native organisms to prosper, as they have few of their enemies. The Galápagos has 1,645 introduced types, many of which are significantly affecting the safety of its endemic ones.

A recent research indicates the non-native amphibians are hungry insect consumers, and might be unevenly consuming uncommon insects found exclusively on the archipelago, or depleting the food sources of the islands' rare avian species, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

The Galápagos frogs have shown some atypical characteristics, including surviving in slightly salty water, which is rare for amphibians.

Their metamorphosis stage is also extremely inconsistent, with some tadpoles becoming frogs very rapidly and others taking a long time: San José observed one which stayed as a tadpole in her lab for half a year.

"We really don't know this aspect," she says, worried the larvae could be impacting the region's freshwater, a very limited resource in Galápagos.

Techniques to curb the frogs in the beginning of the century were largely unsuccessful. Conservation officers tried collecting large numbers by hand and slowly raising the salt content of lagoons in vain.

Studies indicates applying caffeine – which is highly poisonous to amphibians – or using electrocution could help, but these methods aren't necessarily safe for other uncommon Galápagos species.

Without solutions to more of the basic questions about their biology and impact, culling the frogs might not even be the correct way to proceed, says San José.

Financial Obstacles for Study

While she expects the growing use of eDNA methods and DNA analysis will assist her team make sense of the invasive species, funding for the research has been difficult to obtain.

"Everybody wants to give funding for preserving frogs," says San José. "But it's more difficult to find funding for an invasive frog that you might want to control."