Coqui frogs sound larger than they look. The adults measure just a couple of inches from head to tail, and the babies are about the size of a fingernail. But when the males decide its time to find a friendly female and make some little froggy babies, they aren't shy about advertising their goods. Perhaps it's because they're so loud and so hard to spot that trying to find them is such a frustrating task.
Last month I was on an expedition with herpetologist Greg Pauly from the Natural History Museum of LA and a dozen citizen scientists. Our mission was to track down as many frogs as possible.
But we weren't looking for the frogs in the streams of the Santa Monica Mountains or the ponds of the San Gabriels, as you might expect. We were inside a warm, moist greenhouse at a wholesale nursery in Torrance.
Coqui frogs (Eleutherodactylus coqui), named for their distinctive mating call (ko-KEE) are native to Puerto Rico. Take a stroll through the Santa Monica Mountains and if you're patient you might be able to find a Pacific chorus frog or a California tree frog. Western toads are also native to these parts, and if you're really lucky you might stumble upon a California red legged frog, another amphibian Angeleno that's the focus of a reintroduction effort by National Park Service biologists. But you won't find any coqui frogs. At least not yet.
They have become quite common in Florida (though what non-native reptile or amphibian isn't common in Florida by now?) and became invasive on Hawaii's big island sometime in the late 1980s. They then spread to Oahu, Kauai, and Maui.
The invaders first hopped onto Hawaii's shores thanks to the nursery trade. Their tiny eggs stowed away on some tropical plants imported to the archipelago from Florida or Puerto Rico. Unlike many frogs, coquis don't have a tadpole stage; they emerge from their eggs as tiny froglets, which in part allows them to be such good invaders. An egg mass, or even a gravid female, can hitch a ride on a potted plant and end up halfway across the world, ready to found a new population.
The problem is that unlike in Puerto Rico, the frogs don't have any natural predators in Hawaii. Unless controlled by humans, they're free to be fruitful and multiply. In some places, their density has been estimated as high as 10,000 per acre. They could gobble up some 50,000 insects each night, negatively impacting the Hawaiian ecosystems that have come to rely on those bugs.
At home, Puerto Ricans cherish the familiar call of eager males as a part of their natural heritage, but in Hawaii the hoppers are considered a nuisance. The nocturnal chorus causes people complain of lost sleep. Some compare the frogs' chirps to the sound of a jet engine, and it's not an entirely ridiculous assessment. Despite their diminutive size, the critters produce sounds around 90 decibels. According to researchers from Purdue University, that's roughly how loud a Boeing 737 would sound if it was some 6,000 feet overhead, or the sound of a motorcycle engine 25 feet away. It's probably not enough to cause serious physical pain unless it's prolonged, but it's certainly enough to become psychologically and emotionally painful. Especially if it's keeping you up at night.
The froggy invaders don't just diminish sleep quality. According to a 2006 study, property values can even decline in areas of high coqui density to the tune of 0.16 percent. On the Big Island, that would represent a combined loss of about $7.6 million dollars if the frogs spread to all residential neighborhoods. And that doesn't include economic losses from the destruction of plants in the nursery trade to guard against further importations, nor from reductions in the aesthetic appeal of properties that have had their landscaping destroyed in attempts to eradicate the frogs.
It's perhaps easy to see why it's worrisome that coqui frogs have started to turn up in Los Angeles. On one hand, it's not all that surprising. Los Angeles is home to two of the busiest ports in the world, and we have no shortage of non-native reptiles and amphibians setting up shop in our neighborhoods, from the earthworm-like brahminy blind snake to the distinctive green anole.
In just two hours, our group collected more than 100 coqui frogs inside of a single greenhouse. From the sound of their chirps, we knew that there were still at least a few frogs we'd missed. Here in California, there are established populations in Orange and San Diego counties. It isn't clear yet whether the coquis have spread beyond the one nursery in Torrance yet, and it is equally unclear whether anything could be done if they do. Despite all its efforts and millions of dollars spent, the big island seems to have given up any attempts at containment or eradication. The problem is simply too big.
The large-scale movement of wildlife around the world is in many ways the new normal. While wildlife officials can implement precautions, tiny stowaways will still pass their checkpoints either unintentionally through mechanisms like the nursery trade, or intentionally thanks to the pet trade. It will be up to us to decide how to respond when an interloper arrives on our doorstep.
Meanwhile, for those 100 frogs we caught on that summer night in Torrance, their story ends with their contribution to science. They're now a permanent part of the Natural History Museum's herpetology collection, where they will enable researchers both now and in the future to understand the complex ways in which our species has changed the world.