Coqui Frogs Are Coming to Oahu

Shrieking, invasive, miniature frogs have overrun the Big Island. Now they want Oahu.

Every evening, as darkness falls across the lush east side of the Big Island, thousands upon thousands of tiny coqui frogs fill the night with their piercing, unrelenting ko-KEE-ko-KEE-ko-KEE mating call.

The racket has disrupted untold hours of sleep, scared off home buyers, plagued the nursery industry and shattered the tranquility of the East Hawaii night forever.

It also foreshadows what’s in store for us.

The coquis are coming, Oahu, and if they overwhelm the preciously thin line of defense that has kept their population from exploding here so far, no green valley or well-watered yard on the island will be immune to their dreadful call.

The Big Island, which has given up any hope of eradicating them, now serves as a giant reservoir from which coquis are constantly escaping via interisland barges and aircraft. They’ve landed on all the Neighbor Islands, stowing away in nursery shipments, car bumpers, the cut orchids you carried on the plane with you from Hilo, anywhere they can find a dark, damp nook.

The tiny amphibians—they’re about the size of a quarter, with frog legs attached—are turning up on Oahu with increasing frequency. Five years ago, the state’s Pest Hotline hardly ever rang with reports of coquis on this island. Now it rings once or twice a month. When it does, a frog-busting team is dispatched to the scene—and often it’s the same scene over and over again. It’s a giant game of Island-wide coqui Whac-a-Mole: get ’em here, they pop up over there, get ’em there, they pop back up over here.

“We’ve had to invent the word ‘re-eradicate,’ because that’s what we keep doing here,” says Christy Martin, spokesperson for the Coordinating Group on Alien Pest Species, a partnership of government and private agencies trying to hold off a full-scale coqui invasion of Oahu.

So far, the discoveries of coqui on Oahu have mostly been limited to plant nurseries and residential areas, where the frogs have been easy to get at. They do, after all, tend to draw attention to themselves. In small numbers, they’re manageable. The big fear is that they’ll get into remote parts of the Koolau Mountains or the Waianae Mountains, where they will breed faster than anybody can whack them down.

“If they start climbing the mountains,” Martin says, “there’s nothing we can do to stop them.”

If you call the state’s Pest Hotline to report a coqui frog on Oahu, you’re likely to get a house call from Keevin Minami, a vertebrate specialist with the state Department of Agriculture.

He’s been dubbed the Coqui Whisperer for his spot-on coqui imitation, a ko-KEE whistle so convincing that male coquis within earshot—territorial creatures that they are—feel obliged to answer. Equipped with an LED headlamp and a clear plastic tube with a Gatorade bottle affixed to the end, Minami will mimic a frog until he zeros in on its location. This can take hours. When he finally spots it, he slips the tube over it, taps it into the bottle, and takes it back to his office to live out its life in a terrarium.

“I always try to bring my man back alive,” he says.

Minami and two colleagues have caught well over a hundred coqui in neighborhoods all over the island, from Kailua to Kapolei, Haleiwa to Hawaii Kai. He’s combed the landscaping of mansions at Diamond Head and Portlock, he’s staked out foliage in Waikiki into the wee hours of the morning, he’s stalked frogs in the garden department of Home Depot, and time after time he’s been called back to plant nurseries in Waimanalo, a perennial coqui hot spot.
 

In the wild, coquis grow to about an inch. In UH entomologist Arnold Hara’s laboratory, they can grow much larger.

“The adrenaline when you catch them is unreal,” Minami says. But he’s driven by more than just the thrill of the hunt. He’s well aware of his personal stake in the battle. He lives near a forested area in Aiea Heights, and he’s a light sleeper.

A young female coqui can lay a clutch of eggs every 2.5 weeks, producing more than 1,400 eggs per year. The babies hatch as fully-formed froglets, skipping the tadpole stage.

“Even when the birds start singing, I wake up,” he says. “I don’t want these frogs up there.”

Not all of Oahu’s coqui incursions have been small enough for a few guys with flashlights and plastic bottles to deal with. In Hauula, coquis had spread to several yards and a public park before anyone thought to call the Pest Hotline (residents mistook the chirping frog for an obnoxious, new nocturnal bird). There have been multiple infestations in and around Waimanalo’s plant nurseries.

When an area has more coquis than anybody can catch by hand, it’s doused with citric acid, the only federally-approved chemical for coqui control.

Oahu’s worst coqui outbreak to date occurred in Wahiawa, where, around 2001, the frogs spread from a small backyard nursery across a neighborhood and into a military training area at Schofield Barracks. Workers thinned about five acres of brush on the base and soaked the trees and ground with citric acid pumped through fire hoses. They marched through the neighborhood in chemical suits, spraying citric acid from backpack-mounted tanks. They sprayed every few weeks, for five years, before the frogs were finally silenced and the operation was declared a success, in 2008.

“The crew would work until 10 at night, and the residents were very tolerant of us,” says Rachelle Neville, coordinator of the Oahu Invasive Species Committee. “If they had put up a stink, we might not have succeeded.”

At its height, the Wahiawa infestation included about 150 calling male frogs.

In the laboratory, female coquis can lay some 50 eggs every two to three weeks. Unlike other frogs, the coqui has no tadpole stage. Babies hatch as fully formed froglets, their range unhindered by the need for standing water that tadpoles have. In about eight months, the little hatchlings become breeding adults.

The coqui’s incessant call, repeated every few seconds, explodes from its tiny body at up to 95 decibels. That’s louder than an alarm clock, a barking dog or your average leaf blower. If you had to work with something that loud right next to your head, the Occupational Safety and Health Administration would make you wear hearing protection.

The females aren’t the noise makers. They rasp quietly, unnoticed by anyone but other coquis. It’s the males that make all the racket. Their two-note ko-KEE call is part macho bluster, part love song. The low-note ko is a warning to other males to keep their distance (it also helps them distribute themselves evenly through the foliage). The high-note KEE is the call to reproductive action. Ko-KEE could, therefore, be translated as, “Keep your distance, bruddahs / Ladies, I’m yours.” 
 

The “coqui cooker” kills frogs hiding in nursery shipments leaving the Big Island.

Their populations grow exponentially. In the most densely infested parts of the Big Island, the number of coquis can exceed 10,000 per acre.

Odd as it may seem to anybody in Hawaii who has ever been driven into the yard in the middle of the night to squelch a chirping frog outside the bedroom window, the coqui is actually beloved in its native homeland, Puerto Rico. It’s the national amphibian there, a symbol of Puerto Rican pride, celebrated in myth, song and souvenirs.

People aren’t the only ones in who appreciate coquis in Puerto Rico. Snakes, tarantulas, giant spider crabs and a host of other predators not found in Hawaii like them, too. These predators keep coqui numbers in check, and distinguish Puerto Rico’s loveable, limited coquis from East Hawaii’s uncurbed infestation. (In Hawaii, chickens, mongoose, rats and even cats have been known to eat coquis, but nothing is eating the frogs fast enough to make a difference.)

When heard from a distance, a chorus of coqui frogs has a melodious quality. When 10,000 coquis drown out normal human speech, even a Puerto Rican might complain.

Researchers have been looking for ways to control coquis since the late 1990s. Hydrated lime was used for a while, but ran afoul of federal pesticide regulations, as did caffeine spray, which gave the frogs heart attacks (and gave coffee lovers pause). Chytrid fungus, a natural pathogen that has been decimating other amphibians all over the world, turned out to be harmless to coquis. Pesticides, parasites, soaps, surfactants, Tylenol and nicotine have all come up short as coqui-control agents. Recent research at UH-Hilo has found that Prozac suppresses coqui libido and aggression, leaving the frog no reason to chirp. But how 10,000 frogs might be put on an antidepressant has yet to be worked out.

University of Hawaii entomologist Arnold Hara has proposed sterilizing massive numbers of male coquis through irradiation, then releasing them into the wild, a population-control technique that been used successfully on insects such as the Zanzibar tsetse fly. He’s yet to find funding for the research.

Hara has been looking for ways to stop the spread of coquis frogs for more than a decade. He’s come up with some wild ideas, such as dumping high volumes of seawater onto coqui-infested habitat, burning down the habitat altogether, and praying for either a severe drought or a freeze to strike Hilo. He’s also discovered that water heated to 113 degrees and sprayed on infested plants for five minutes kills both coquis and their eggs. “It’s just a hot shower,” he says. “That’s all they need.”

Big Island nurseries now use Hara’s “coqui cooker”—a shipping container transformed into a plant shower—to treat shipments of plants before sending them off-Island. The state Department of Agriculture has built its own cooker to treat contaminated material it finds at Honolulu Harbor.

Although Hara concedes that the coqui is in Hawaii to stay, ultimately, he believes, with or without help from science, nature will knock its population down to more tolerable levels. “Eventually, there’s going to be a disease, or a parasite, or some other controlling biological factor,” he says.

When that might happen is anybody’s guess. Presuming it does happen, and once everyone who grew up in Hawaii in the pre-coqui era is replaced by a new generation that never knew the quiet of a Hawaiian night, then perhaps our coqui problem will be a thing of the past.

In the meantime, Oahu, brace yourself.