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During her regular walk to the research facility, scientist Miriam San José stoops near a small pond surrounded by dense vegetation and collects a small plastic sound device.

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

Despite abounding with remarkable animals – such as ancient giant tortoises, marine iguanas, and the well-known finches that sparked Darwin's evolutionary theory – the Galápagos archipelago off the coast of South America had long remained free of amphibians.

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, through time, there have been repeated unintentional arrivals to the islands, and the frogs now have a strong presence on two islands: multiple locations.

The population is expanding so rapidly that researchers have been finding it difficult to keep track, estimating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José tagged amphibians and attempted to recapture them in the subsequent 10 days, she could find only a single tagged frog occasionally, indicating their numbers were enormous.

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

Deafening Noise and Growing Concerns

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

For the scientists, their nocturnal vocalizations are useful in determining their existence in far-flung areas, using audio devices like the one outside San José's workplace.

But nearby farmers 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 a local coffee farmer from the island.

"Initially it was a shock, observing the initial frogs in the area," says Larrea Saltos, who started observing their large numbers about three years ago when one leaped on her hand as she was stepping out of her front door.

Ecological Impact Stays Unknown

The noise isn't the primary problem, though. While the species has been in the islands for almost 30 years, experts still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

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

A recent study suggests the non-native frogs are voracious insect eaters, and might be disproportionately eating uncommon insects found only on the islands, or depleting the food sources of the islands' uncommon birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island amphibians have exhibited some unusual traits, including surviving in brackish water, which is rare for amphibians.

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

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

Techniques to control the frogs in the early 2000s were largely ineffective. Conservation officers tried collecting significant quantities by hand and gradually increasing the salt content of ponds in vain.

Research indicates spraying caffeine – which is extremely poisonous to amphibians – or using electrocution could help, but these methods aren't always secure for other rare Galápagos organisms.

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

Financial Obstacles for Research

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

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