SCHOFIELD BARRACKS — It's hard to imagine a tiny, 2-inch frog could cause so much harm.

Beloved in its native Puerto Rico, the coqui frog has become a menace in Hawai'i, where it suddenly appeared in the late 1990s. With no natural predators, such as snakes, to keep their numbers under control, the frogs and their loud "ko-KEE" mating calls have multiplied exponentially — causing headaches for homeowners.

Some believe the noisy amphibians could also cause serious damage to Hawai'i's economy if they drag down housing prices, which real-estate agents say is a distinct possibility. Officials have begun an extermination effort on several islands, hoping to get the problem under control before long-term economic losses set in.

"This is an invasive species of the worst kind," said state Rep. Clifton Tsuji, whose Big Island constituents endure choruses of crying coqui in their backyards. "It's a species of mass destruction."

Experts believe the first frog — or frogs — hitched a ride to Hawai'i in a plant shipped from Puerto Rico or Florida. Hawai'i's year-round temperate weather and open space provided the coqui with an ideal environment in which to reproduce.

Now, some parts of the Big Island have infestations so large, authorities have been forced into containment mode, abandoning ambitions to eradicate the frogs.

Brooks Kaiser, a University of Hawai'i visiting scholar heading an economic impact study of the coqui, said living next to a major infestation could rival the experience of living next to an airport. Residents, for the most part, agree.

Mac Lowson, president of the Hawaii Association of Realtors, said he is particularly vulnerable to the noise in his town of Kapalua on Maui because he suffers from hyperacusis, a condition that makes him highly sensitive to sounds.

"I would rather probably live next to a highway rather than live next to an area that has the coqui frogs. The coqui frog (sound) is a shrill shriek and then silence," Lowson said. "A highway is more of a continuous rumble and there is something you can do with it."

On the east side of the Big Island, where the coqui infestations are the most serious, real-estate prices have surged between 24 percent and 36 percent in a year, said Reid Choate, a real-estate appraiser specializing in the area.

"The market's red hot. What's going to happen when the market isn't so red-hot?" Lowson asked. "The houses that people are going to buy are those that don't have the coqui frogs around."

Evidence is already starting to crop up showing the potential for problems.

Sixty-two percent of Big Island real-estate agents surveyed last year by University of Hawai'i professor Arnold Hara said they were involved in deals affected in some way by the presence of coqui. Nine of the 53 real-estate agents said they had handled cases in which home buyers backed out of contracts because the frogs were too loud. One said the presence of coqui had dragged down home prices in an entire subdivision.

The frogs have yet to turn up in big numbers on O'ahu. Scott Williamson, an invasive species biologist with the state Department of Land and Natural Resources, said authorities are so worried about how serious the problem there could become, they are taking an aggressive approach.

Officials spray the frogs with a deadly mixture of citric acid and water at least four nights a week in the area around the Schofield Barracks Army base, where their numbers are concentrated. The state has also stepped up money to exterminate the frog, allocating $300,000 to the counties this year.

"O'ahu's in the shape that Big Island was say eight, 10 years ago when they first started noticing them," Williamson said. "A few biologists said this is going to be a problem because they have the potential to breed anywhere almost in Hawai'i. ... But nobody really paid any attention. Nobody thought a frog could be a problem."