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On her regular walk to the scientific station, biologist Miriam San José crouches near a small pond covered by dense plants and collects a compact green sound device.

She had placed there through the night to record the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an invasive threat with effects that experts are starting to understand.

Despite teeming with remarkable wildlife – such as ancient large turtles, marine lizards, and the famous finches that inspired Darwin's theory of evolution – the Galápagos archipelago near the coast of Ecuador had historically been free of frogs and toads.

In the late 1990s, this changed. Several tiny tree frogs made their way from mainland Ecuador to the islands, likely as stowaways on cargo ships.

DNA studies suggest that, through time, there have been repeated accidental introductions to the archipelago, and the amphibians now have a firm presence on two islands: Isabela and Santa Cruz.

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

When San José tagged amphibians and attempted to find them in the following week and a half, she could find just one marked frog occasionally, indicating their populations were enormous.

They estimated 6,000 frogs in a single pond. "The calculations are still very conservative," says San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is clear from the acoustic chaos they cause. "The number of frogs and the sound – it's truly insane," says San José.

For the researchers, their nocturnal vocalizations are helpful in estimating their existence in remote areas, using recorders like the one outside the workplace.

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

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

"At first it was a shock, seeing the first frogs in the region," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was stepping out of her front door.

Environmental Consequences Stays Unclear

The sound isn't the primary problem, however. While the amphibians has been in the islands for almost 30 years, scientists still know limited information about its impact on the archipelago's precariously balanced land and water ecosystems.

On islands, it is very common for invasive species to thrive, as they have none of their enemies. The Galápagos counts over sixteen hundred introduced species, many of which are seriously affecting the survival of its endemic ones.

A recent study suggests the non-native frogs are voracious bug eaters, and might be disproportionately eating rare bugs found exclusively on the islands, or reducing the nutrition of the region's uncommon avian species, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis stage is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a long time: the researcher witnessed one which remained as a tadpole in her laboratory for six months.

"We really don't know this part," she says, concerned the larvae could be impacting the islands' freshwater, a very limited resource in the islands.

Techniques to control the amphibians in the early 2000s were largely unsuccessful. Conservation officers tried collecting significant quantities by hand and slowly increasing the salinity of ponds in without success.

Studies indicates applying caffeine – which is highly poisonous to amphibians – or using electrical methods could assist, but these approaches aren't always secure for other uncommon island organisms.

Without answers to more of the basic questions about their biology and impact, culling the amphibians might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

While she expects the growing use of eDNA techniques and DNA examination will assist her team understand of the invasive species, funding for the research has been difficult to obtain.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an invasive frog that you might want to control."