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On her daily commute to the scientific station, biologist Miriam San José crouches near a shallow water body surrounded by thick vegetation and retrieves a small plastic audio device.

She had placed there through the night to capture the characteristic calls of the Scinax quinquefasciatus, recognized by local scientists as an invasive species with effects that scientists are just beginning to comprehend.

Although abounding with unique animals – such as ancient large turtles, swimming lizards, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain near the coast of South America had long remained free of frogs and toads.

In the late 1990s, this shifted. Several small amphibians made their way from mainland the mainland to the islands, likely as hitchhikers on transport vessels.

DNA research suggest that, over the years, there have been repeated accidental arrivals to the islands, and the frogs now have a strong presence on two locations: Isabela and Santa Cruz.

The numbers is growing so quickly that researchers have been struggling to monitor, estimating populations in the millions on each island, across developed and farming areas, but also in the protected natural reserve.

When the biologist tagged frogs and attempted to recapture them in the subsequent 10 days, she could locate only a single marked frog from time to time, indicating their numbers were enormous.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states San José. "I'm pretty sure there are even more."

Acoustic Chaos and Rising Worries

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

For the researchers, their nightly vocalizations are useful in estimating their presence in far-flung areas, using recorders like the one outside San José's workplace.

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

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

"Initially it was a shock, observing the first frogs in the area," says the farmer, who started observing their large numbers about several years ago when one jumped on her hand as she was stepping out of her front door.

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, however. While the species has been in the islands for nearly 30 years, scientists still know limited information about its effect on the islands' precariously balanced terrestrial and aquatic environments.

On archipelagos, it is very common for invasive organisms to thrive, as they have few of their natural predators. The islands has over sixteen hundred introduced species, many of which are seriously disrupting the safety of its endemic ones.

A recent study indicates the non-native frogs are hungry insect consumers, and might be unevenly consuming rare bugs found only on the islands, or depleting the food sources of the islands' uncommon birds, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos frogs have exhibited some atypical characteristics, including living in brackish water, which is rare for frogs.

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

"We really don't know this aspect," she says, concerned the tadpoles could be impacting the region's clean water, a very limited resource in Galápagos.

Techniques to curb the frogs in the beginning of the century were largely unsuccessful. Park rangers tried collecting large numbers by hand and slowly increasing the salinity of ponds in vain.

Research suggests applying coffee – which is highly poisonous to frogs – or using electrocution could help, but these methods aren't necessarily secure for other rare island species.

Lacking solutions to more of the basic questions about their biology and effect, removing the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the growing use of eDNA methods and genetic analysis will help her group understand of the invasive species, funding for the project has been hard to come by.

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