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

She had placed there overnight to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos researchers as an invasive species with effects that scientists are starting to comprehend.

Although abounding with unique wildlife – such as centuries-old giant tortoises, marine lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the shoreline of Ecuador had long remained free of frogs and toads.

In the late 1990s, this changed. Several tiny amphibians made their way from continental the mainland to the islands, probably as hitchhikers on cargo ships.

Genetic studies indicate that, over the years, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a strong foothold on two locations: multiple locations.

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

When the biologist marked amphibians and attempted to find them in the following week and a half, she could locate only a single marked frog from time to time, suggesting their numbers were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," says San José. "I'm quite certain there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the acoustic chaos they cause. "The amount of frogs and the sound – it's truly insane," comments San José.

For the researchers, their nightly mating calls are useful in determining their presence in far-flung areas, using recorders like the one near San José's workplace.

But nearby agricultural workers say the sounds are so raucous they prevent sleep at night.

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

"At first it was a surprise, seeing the first frogs in the area," says Larrea Saltos, who started observing their abundance about several years ago when one jumped on her hand as she was stepping out of her house.

Ecological Impact Remains Unclear

The noise isn't the primary problem, however. While the species has been in the Galápagos for nearly 30 years, scientists still know limited information about its impact on the archipelago's delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for invasive organisms to prosper, as they have none of their enemies. The Galápagos counts over sixteen hundred invasive types, many of which are significantly affecting the safety of its endemic ones.

A 2020 research indicates the invasive frogs are hungry insect consumers, and might be disproportionately eating uncommon insects found only on the archipelago, or depleting the food sources of the islands' rare birds, affecting the food chain.

Unique Characteristics and Control Challenges

The island frogs have exhibited some unusual traits, including living in slightly salty water, which is rare for amphibians.

Their development process is also extremely variable, with some tadpoles becoming frogs very quickly and others taking a long time: San José observed one which remained as a tadpole in her lab for half a year.

"We truly don't know this aspect," she says, concerned the tadpoles could be affecting the islands' clean water, a very scarce resource in Galápagos.

Techniques to control the frogs in the early 2000s were mostly ineffective. Park rangers tried collecting significant quantities by manual methods and slowly increasing the salinity of lagoons in vain.

Studies indicates applying coffee – which is highly toxic to amphibians – or using electrocution could assist, but these methods aren't always safe for other uncommon island species.

Lacking answers to more of the fundamental issues about their biology and effect, culling the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she expects the growing use of eDNA techniques and DNA examination will help her group make sense of the invasive species, financial support for the project has been difficult to come by.

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