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On her regular commute to the scientific station, biologist Miriam San José stoops near a small water body covered by dense plants and collects a small green sound device.

The device was left there through the night to capture the distinctive croaks of the Scinax quinquefasciatus, recognized by local researchers as an invasive threat with effects that experts are starting to understand.

Despite abounding with remarkable wildlife – such as ancient giant tortoises, marine lizards, and the famous finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had historically been free of frogs and toads.

During the 1990s, this changed. Several tiny amphibians made their way from continental Ecuador to the islands, probably as stowaways on cargo ships.

Genetic research suggest that, over the years, there have been multiple accidental arrivals to the archipelago, and the frogs now have a strong foothold on several locations: multiple locations.

The population is growing so quickly that scientists have been finding it difficult to monitor, estimating numbers in the hundreds of thousands on each island, across urban and agricultural areas, but also in the protected Galápagos national park.

When the biologist tagged frogs and attempted to recapture them in the following week and a half, she could find only a single tagged frog occasionally, suggesting their numbers were enormous.

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

Deafening Noise and Rising Worries

The frogs' proliferation is evident from the acoustic chaos they cause. "The number of frogs and the sound – it's really incredible," comments the scientist.

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

But nearby farmers say the sounds are so loud they prevent sleep at night.

"During the wet season, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

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

Environmental Consequences Stays Unclear

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

On islands, it is very typical for non-native organisms to thrive, as they have none of their natural predators. The islands has 1,645 invasive species, many of which are significantly disrupting the safety of its native ones.

A 2020 research indicates the invasive amphibians are voracious bug consumers, and might be disproportionately eating uncommon insects found exclusively on the islands, or depleting the food sources of the islands' rare birds, affecting the food chain.

Unusual Traits and Control Challenges

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

Their development stage is also highly inconsistent, with some larvae turning into frogs very quickly and others taking a long time: San José observed one which stayed as a tadpole in her lab for half a year.

"We truly don't know this aspect," she says, concerned the larvae could be impacting the region's freshwater, a very scarce resource in the islands.

Techniques to control the amphibians in the early 2000s were mostly unsuccessful. Park rangers tried collecting significant quantities by hand and gradually increasing the salt content of ponds in vain.

Studies indicates applying coffee – which is extremely toxic to amphibians – or using electrical methods could assist, but these approaches aren't necessarily secure for other rare Galápagos organisms.

Without solutions to more of the basic questions about their biology and impact, culling the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she expects the increasing use of environmental DNA techniques and DNA analysis will assist her team understand of the invader, funding for the project has been hard to come by.

"Everybody wants to give funding for preserving frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."