Pillaging native forests, screeching through the night in suburban neighborhoods and rooting around in rural taro patches, wild animals of Hawai'i's ancient past and globalized present abound across the Islands.

Species such as hybrid Polynesian pigs and a newly discovered gall wasp have eluded eradication efforts and taken hold in the ecosystem.

Some, like the vocally endowed coqui frog from Puerto Rico, arrived by accident.

Others — like the Big Island's wild horses and cattle, Moloka'i's resident goats and Honolulu's legions of feral felines — were released deliberately for hunting or broke free from the two-legged residents who brought them.

In the Islands' warm, moist, environment, some invasive species have flourished and helped push out the species that evolved in Hawai'i.

Hawai'i today has more than 300 endangered and threatened plant and animal species accounting for about one-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 O'ahu. Earlier this year, one Big Island taro farmer acknowledged shooting dead several wild horses that had damaged his crops.

Despite all this, not everyone feels they all need to be wiped out.

TO KILL OR NOT TO KILL

"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 Hawai'i," said Cathy Goeggel, Animal Rights Hawai'i director.

Goeggel advocates fencing out and relocating the problem animals, such as rooting pigs.

Hawai'i 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 at Ka'ena Point State Park.

"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.

ENDEMIC SPECIES FADING

There are about 9,975 endemic species living in the Islands. Another 1,100 endemic species once lived here but 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 Hawai'i, only about 300 to 500 have gone on to wreak significant damage and some, including agricultural plants, are even beneficial, he said.

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 Hawai'i isn't minty. Nettles don't have stings. And unlike their continental cousins, Hawai'i's native variety of raspberry doesn't have prickles.

That means native raspberry plants aren't tough enough to withstand the ground foraging of non-native animals such as pigs — which opens the door for foreign varieties of raspberries well-equipped to stand up against such adversaries.

"It's the mix of everything that builds and exacerbates a problem even further," Campbell 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," 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 including The Nature Conservancy, National Park Service and the Hawai'i Visitors Bureau.