HONOLULU In Hawaii's warm, moist environment, interlopers have flourished.
Known as invasive species, they pillage native forests, screech through the night in suburban neighborhoods and root around in rural taro patches.
Stealthy, unwelcome species such as hybrid Polynesian pigs and a newly discovered gall wasp have eluded eradication efforts and taken hold in an ecosystem that was once home to only one terrestrial mammal, an insectivorous bat.
Some nonnative animals, like the vocally endowed coqui frog from Puerto Rico, arrived by accident.
Others like the Big Island's wild horses and cattle, Molokai's resident goats and Honolulu's legions of feral felines were released deliberately for hunting or broke free from the residents who brought them.
Partly as a result of these island interlopers, Hawaii today has more than 300 endangered and threatened plant and animal species accounting for about a quarter of the nation's protected species.
Humans have strengthened their defenses against the animals, spraying lethal citric acid to kill coqui frogs and setting out traps for pigs in suburban Oahu. One Big Island taro farmer publicly acknowledged earlier this year that he shot and killed several wild horses that had damaged his crops.
Still, despite the annoyances and ecological upheaval these introduced animals and plants have caused here, not everyone feels they all need to be wiped out.
"I think semantics plays a big role in this. The term 'invasive species' makes one think that the hordes are at our gates and threatening to destroy life as we know it, when actually the animals who are considered invasive for the most part had no say in coming to Hawaii," said Cathy Goeggel, Animal Rights Hawaii director.
Goeggel advocates fencing out and relocating the problem animals, such as rooting pigs.
Some sympathetic residents even help the survival of nonnative animals, setting out food for cats, including those known to prey upon colonies of native birds on Maui.
Hawaii wildlife officials, however, made their own stance on the feral pet issue clear earlier this month.
State-hired hunters on Nov. 6 shot and killed four dogs believed to have slain at least 113 fledgling wedge-tailed shearwaters inside an Oahu nature reserve.
"Pets that are abandoned or left to run loose in a Hawaiian ecosystem become predators with catastrophic results," said Peter Young, chairman of the Department of Land and Natural Resources, following the shootings.
There are about 9,975 endemic species living in the islands. Another 1,100 endemic species disappeared as invasive species showed up, said Earl Campbell, who heads the Invasive Species Division of the U.S. Fish and Wildlife Service's regional office in Honolulu.
Of the approximately 5,000 alien species in Hawaii, only about 300 to 500 have gone on to wreak significant damage and some, including plants, are even beneficial, he said.
Still, the problem of invasive species looms much larger in isolated island environments than on the mainland.
"If you look at factors that cause problems for species, invasives are important in many places. But here it is the primary reason right now that things are declining," Campbell said.
That's in part because the islands' native inhabitants have evolved without the defenses needed to fend off the aggressive attackers and competitors they now face, he said.
Mint in Hawaii isn't minty. Nettles don't have stings. And unlike their continental cousins, Hawaii's native variety of raspberry doesn't have prickles.
That means native raspberry plants aren't tough enough to withstand the ground foraging of nonnative animals such as pigs.
At the center of it all are people who need to recognize their mistakes and think more about how to make things better, said Christy Martin, spokeswoman for the Coordinating Group on Alien Pest Species, a partnership that brings together a long list of federal, state and private agencies.
"There's definitely a disconnect between caring for animals and setting up cat feeding stations, and protecting the ones that are native, that are supposed to be there, that need our help definitely more than the cats do," Martin said.
Human-introduced invasive animals began with rats that tagged along on Polynesians' voyaging canoes and continued in the mid to late 1800s when quick-spreading haole koa was planted to provide fodder for cattle in the islands, she said.
"If only we'd chosen better. And we say that again and again," she said.
There are programs and rules to keep potentially invasive animals out of the islands. But there's nothing comparable to keep potentially invasive plants from being imported and planted in Hawaiian gardens.
It would be too difficult, costly and controversial to eliminate established invasive animals such as pigs and goats that live in hard-to-reach places and are hunted by some poorer residents to feed their families. Efforts now are concentrated on controlling the old invasive species, fighting off the newer ones, keeping the would-be problems out and continuing to educate the public.
"I don't want this much job security," Martin said with a slightly nervous laugh. "But I clearly have it."