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During her regular walk to the scientific station, biologist Miriam San José stoops near a shallow water body surrounded by thick vegetation and retrieves a small green sound device.

The device was left there through the night to capture the distinctive croaks of the Scinax quinquefasciatus, known by local scientists as an non-native species with consequences that experts are just beginning to understand.

Despite abounding with remarkable wildlife – such as ancient large turtles, swimming iguanas, and the famous finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had historically been devoid of frogs and toads.

In the late 1990s, this shifted. Several tiny tree frogs traveled from mainland the mainland to the archipelago, probably as stowaways on transport vessels.

Genetic studies suggest that, through time, there have been repeated unintentional arrivals to the archipelago, and the amphibians now have a strong presence on several locations: Isabela and Santa Cruz.

The population is expanding so quickly that scientists have been struggling to keep track, estimating numbers in the millions on every island, across developed and agricultural areas, but also in the protected natural reserve.

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

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very low," says the researcher. "I am quite certain there are even more."

Deafening Noise and Rising Worries

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

For the scientists, their nightly vocalizations are helpful in determining their existence in remote areas, using recorders like the one outside San José's office.

But nearby agricultural workers say the calls are so raucous they keep them up at night.

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

"At first it was a surprise, seeing the first frogs in the area," says Larrea Saltos, who started noticing their large numbers about three years ago when one leaped on her palm as she was stepping out of her house.

Environmental Consequences Stays Unknown

The noise isn't the primary problem, though. While the species has been in the Galápagos for nearly 30 years, scientists still know very little about its effect on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very common for invasive organisms to thrive, as they have none of their natural predators. The Galápagos counts 1,645 introduced types, many of which are seriously disrupting the safety of its native ones.

A recent research indicates the invasive frogs are voracious bug eaters, and might be unevenly eating uncommon bugs found exclusively on the archipelago, or depleting the food sources of the islands' rare avian species, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

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

Their metamorphosis process is also highly variable, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher witnessed one which stayed as a tadpole in her laboratory for half a year.

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

Techniques to control the frogs in the early 2000s were largely unsuccessful. Conservation officers tried capturing significant quantities by hand and gradually raising the salinity of lagoons in without success.

Research suggests applying caffeine – which is highly poisonous to frogs – or using electrocution could assist, but these approaches aren't necessarily safe for other uncommon Galápagos species.

Lacking answers to more of the fundamental questions about their lifestyle and effect, removing the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she hopes the growing use of eDNA techniques and genetic analysis will help her team understand of the invasive species, funding for the project has been difficult to obtain.

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