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During her regular walk to the scientific station, scientist Miriam San José stoops near a shallow water body covered by dense plants and retrieves a small plastic sound recorder.

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

Although teeming with unique animals – such as ancient giant tortoises, marine lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the island chain off the coast of South America had long remained devoid of frogs and toads.

During the 1990s, this shifted. Several small tree frogs made their way from continental Ecuador to the archipelago, likely as stowaways on cargo ships.

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

The numbers is expanding so rapidly that scientists have been finding it difficult to monitor, calculating populations in the millions on each island, across developed and agricultural areas, but also in the conservation Galápagos national park.

When the biologist tagged amphibians and attempted to recapture them in the following week and a half, she could locate just one tagged frog from time to time, suggesting their populations were massive.

They estimated six thousand frogs in a single pond. "Our estimates are still very conservative," says the researcher. "I am quite certain there are even more."

Acoustic Chaos and Growing Concerns

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

For the scientists, their nocturnal vocalizations are helpful in estimating their existence in far-flung areas, using audio devices like the one near San José's office.

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

"During the rainy period, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

"At first it was a shock, seeing the initial frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one jumped on her palm as she was walking out of her front door.

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, however. While the amphibians has been in the islands for almost 30 years, experts still know limited information about its effect on the archipelago's delicately balanced land and water ecosystems.

On archipelagos, it is very typical for invasive species to prosper, as they have few of their enemies. The Galápagos counts over sixteen hundred invasive species, many of which are significantly affecting the safety of its endemic ones.

A recent study suggests the invasive frogs are voracious bug consumers, and might be unevenly eating rare bugs found exclusively on the archipelago, or depleting the food sources of the region's uncommon birds, affecting the food chain.

Unusual Traits and Control Challenges

The island amphibians have exhibited some atypical traits, including living in brackish water, which is rare for frogs.

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

"We really don't know this part," she says, worried the tadpoles could be affecting the islands' clean water, a very limited commodity in the islands.

Methods to control the amphibians in the early 2000s were mostly unsuccessful. Park rangers tried collecting large numbers by manual methods and slowly increasing the salt content of lagoons in without success.

Research indicates applying caffeine – which is highly poisonous to frogs – or using electrocution could help, but these methods aren't necessarily safe for other uncommon Galápagos organisms.

Without answers to more of the fundamental questions about their lifestyle and impact, culling the frogs might not even be the right way to proceed, says the biologist.

Financial Obstacles for Study

While she expects the growing use of eDNA methods and DNA analysis will assist her group make sense of the invasive species, funding for the research has been hard to obtain.

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