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During her daily walk to the research facility, scientist Miriam San José crouches near a small water body surrounded by dense vegetation and retrieves a small plastic audio device.

The device was left there through the night to capture the characteristic calls of the Fowler's snouted treefrog, recognized by local scientists as an invasive species with consequences that experts are just beginning to comprehend.

Although teeming with unique animals – including ancient giant tortoises, swimming iguanas, and the famous finches that inspired Charles Darwin's theory of evolution – the island chain near the coast of Ecuador had historically been free of frogs and toads.

In the late 1990s, this changed. Some tiny amphibians traveled from mainland the mainland to the islands, probably as hitchhikers on transport vessels.

DNA research suggest that, over the years, there have been repeated unintentional introductions to the islands, and the amphibians now have a strong presence on several locations: Isabela and Santa Cruz.

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

When the biologist marked frogs and attempted to recapture them in the subsequent week and a half, she could find only a single marked frog from time to time, indicating their numbers were massive.

They calculated six thousand frogs in a single pond. "Our estimates are still very conservative," says San José. "I am pretty sure there are even more."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the sound chaos they cause. "The amount of frogs and the noise – it's truly insane," says the scientist.

For the researchers, their nightly mating calls are useful in estimating their existence in far-flung areas, using audio devices like the one near San José's office.

But local farmers say the sounds are so raucous they prevent sleep at night.

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

"Initially it was a surprise, seeing the first frogs in the area," says Larrea Saltos, who started observing their abundance about three years ago when one leaped on her palm as she was stepping out of her front door.

Environmental Consequences Stays Unknown

The noise isn't the fundamental problem, however. While the species has been in the islands for almost three decades, experts still know limited information about its impact on the archipelago's precariously balanced land and water environments.

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

A recent study suggests the non-native frogs are voracious insect eaters, and might be disproportionately eating rare bugs found exclusively on the archipelago, or reducing the nutrition of the region's rare birds, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their development stage is also extremely variable, with some larvae becoming frogs very quickly and others taking a long time: the researcher observed one which stayed as a larva in her laboratory for half a year.

"We really don't know this aspect," she says, worried the larvae could be impacting the region's freshwater, a very scarce commodity in Galápagos.

Techniques to curb the frogs in the beginning of the century were largely unsuccessful. Park rangers tried collecting large numbers by manual methods and gradually raising the salinity of lagoons in without success.

Research indicates applying caffeine – which is extremely toxic to amphibians – or using electrocution could help, but these methods aren't necessarily safe for other uncommon Galápagos species.

Without solutions to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Research

While she hopes the growing use of eDNA methods and DNA analysis will assist her group understand of the invader, financial support for the research has been hard to come by.

"Everyone wants to give support for preserving frogs," says San José. "But it's more difficult to find funding for an invasive frog that you might want to manage."