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During her regular commute to the scientific station, scientist Miriam San José crouches near a small pond surrounded by dense vegetation and collects a compact plastic sound device.

She had placed there overnight to capture the distinctive calls of the Fowler's snouted treefrog, known by local scientists as an invasive threat with effects that scientists are just beginning to understand.

Despite teeming with remarkable animals – such as ancient large turtles, swimming lizards, and the famous birds that sparked Darwin's theory of evolution – the Galápagos archipelago near the shoreline of South America had historically been devoid of amphibians.

In the late 1990s, this changed. Several small tree frogs traveled from continental the mainland to the islands, likely as hitchhikers on transport vessels.

Genetic studies suggest that, through time, there have been multiple unintentional arrivals to the archipelago, and the amphibians now have a firm foothold on two islands: Isabela and Santa Cruz.

The numbers is growing so rapidly that researchers have been struggling to keep track, calculating numbers in the millions on each island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José marked amphibians and attempted to recapture them in the subsequent 10 days, she could locate just one marked frog occasionally, indicating their populations were massive.

They calculated six thousand frogs in a solitary pond. "The calculations are still very conservative," states the researcher. "I'm pretty sure there are additional numbers."

Deafening Noise and Growing Concerns

The amphibians' abundance is evident from the acoustic chaos they cause. "The amount of frogs and the noise – it's really incredible," comments San José.

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

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

"In the rainy period, I constantly hear their croaks and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, seeing the initial frogs in the region," says the farmer, who started observing their large numbers about several years ago when one leaped on her palm as she was walking out of her house.

Environmental Consequences Stays Unknown

The noise isn't the primary problem, however. While the species has been in the islands for nearly three decades, scientists still know very little 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 few of their enemies. The Galápagos has over sixteen hundred invasive types, many of which are significantly disrupting the survival of its endemic ones.

A recent study suggests the non-native amphibians are voracious bug eaters, and might be disproportionately consuming uncommon insects found exclusively on the islands, or depleting the food sources of the region's uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

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

Their metamorphosis stage is also highly inconsistent, with some tadpoles becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a larva in her laboratory for half a year.

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

Techniques to curb the amphibians in the early 2000s were largely ineffective. Park rangers tried collecting large numbers by hand and gradually increasing the salinity of ponds in vain.

Research indicates spraying caffeine – which is extremely toxic to frogs – or using electrocution could assist, but these approaches aren't always secure for other rare Galápagos organisms.

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

Financial Obstacles for Research

While she expects the increasing use of environmental DNA methods and genetic examination will assist her group make sense of the invader, financial support for the project has been hard to obtain.

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