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On her regular walk to the scientific station, scientist Miriam San José crouches near a small water body surrounded by thick plants and collects a compact plastic sound device.

She had placed there through the night to record the distinctive croaks of the Scinax quinquefasciatus, known by local researchers as an invasive threat with consequences that scientists are starting to understand.

Despite teeming with remarkable wildlife – such as ancient giant tortoises, swimming lizards, and the well-known finches that sparked Darwin's theory of evolution – the island chain off the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this changed. Some tiny tree frogs made their way from continental Ecuador to the archipelago, probably as hitchhikers on cargo ships.

Genetic studies indicate that, through time, there have been repeated unintentional introductions to the islands, and the frogs now have a firm foothold on several islands: multiple locations.

The numbers is expanding so quickly that researchers have been finding it difficult to monitor, estimating populations in the hundreds of thousands on every island, across developed and agricultural areas, but also in the protected Galápagos national park.

When San José marked amphibians and attempted to recapture them in the subsequent week and a half, she could locate just one marked frog from time to time, indicating their numbers were massive.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very low," states the researcher. "I'm quite certain there are even more."

Acoustic Chaos and Rising Worries

The amphibians' abundance is evident from the sound chaos they create. "The number of frogs and the noise – it's really insane," comments San José.

For the scientists, their nightly mating calls are useful in estimating their presence in far-flung areas, using audio devices like the one outside the workplace.

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

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

"At first it was a surprise, seeing the initial frogs in the area," says the farmer, who started observing their large numbers about several years ago when one leaped on her hand as she was stepping out of her front door.

Environmental Consequences Remains Unclear

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly 30 years, scientists still know very little about its effect on the islands' delicately balanced land and water environments.

On archipelagos, it is very typical for invasive species to thrive, as they have few of their natural predators. The Galápagos has 1,645 introduced types, many of which are significantly disrupting the safety of its native ones.

A 2020 research suggests the invasive frogs are voracious insect eaters, and might be disproportionately eating uncommon insects found exclusively on the archipelago, or reducing the food sources of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have shown some unusual characteristics, including living in brackish water, which is uncommon for frogs.

Their development stage is also extremely variable, with some tadpoles turning into frogs very rapidly and others taking a long time: San José observed one which remained as a larva in her laboratory for half a year.

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

Methods to control the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried collecting large numbers by manual methods and gradually increasing the salinity of lagoons in without success.

Studies indicates spraying caffeine – which is extremely toxic to frogs – or using electrical methods could assist, but these methods aren't necessarily secure for other rare island species.

Without solutions to more of the fundamental issues about their biology and impact, removing the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA techniques and genetic examination will help her group understand of the invasive species, funding for the research has been difficult to come by.

"Everyone wants to give support for protecting frogs," says San José. "But it's harder to find financial backing for an invasive frog that you might want to manage."