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During her daily commute to the research facility, scientist Miriam San José stoops near a small pond covered by thick vegetation and collects a compact green sound recorder.

She had placed there overnight to record the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with consequences that experts are starting to understand.

Despite abounding with remarkable animals – such as centuries-old giant tortoises, marine iguanas, and the famous birds that sparked Darwin's theory of evolution – the island chain off the coast of Ecuador had historically been free of frogs and toads.

During the 1990s, this changed. Several tiny tree frogs traveled from continental the mainland to the archipelago, likely as hitchhikers on transport vessels.

Genetic studies suggest that, over the years, there have been multiple unintentional arrivals to the islands, and the amphibians now have a firm foothold on several islands: multiple locations.

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

When San José tagged amphibians and attempted to find them in the following 10 days, she could locate just one marked frog occasionally, indicating their numbers were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very low," says San José. "I am pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is clear from the acoustic chaos they create. "The amount of frogs and the noise – it's really insane," comments the scientist.

For the researchers, their nocturnal vocalizations are useful in determining their existence in remote areas, using audio devices like the one outside San José's office.

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

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

"At first it was a surprise, seeing the first frogs in the area," says the farmer, who started observing their large numbers about three years ago when one leaped on her palm as she was walking out of her front door.

Environmental Consequences Stays Unclear

The noise isn't the fundamental problem, however. While the species has been in the Galápagos for almost three decades, scientists still know very little about its impact on the archipelago's delicately balanced land and water environments.

On islands, it is very typical for non-native species to prosper, as they have none of their enemies. The Galápagos counts over sixteen hundred invasive species, many of which are significantly disrupting the survival of its endemic ones.

A recent research indicates the non-native amphibians are hungry bug consumers, and might be unevenly consuming uncommon insects found only on the archipelago, or reducing the food sources of the islands' uncommon birds, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island frogs have exhibited some unusual characteristics, including surviving in slightly salty water, which is uncommon for frogs.

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

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

Techniques to curb the amphibians in the beginning of the century were mostly ineffective. Park rangers tried capturing large numbers by manual methods and slowly raising the salinity of lagoons in without success.

Research indicates applying caffeine – which is extremely toxic to frogs – or using electrocution could help, but these approaches aren't always secure for other uncommon Galápagos species.

Without solutions to more of the fundamental questions about their biology and effect, culling the amphibians might not even be the correct way to proceed, says the biologist.

Funding Challenges for Research

While she hopes the increasing use of eDNA techniques and DNA analysis will assist her group understand of the invader, financial support for the project has been hard to obtain.

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