Paradise lost: The alien invasion of Hawaii

Supercolonies of little fire ants, an invasive species, are spreading on the islands

Wasmannia auropunctata, also known as little fire ants.
Hawaii Department of Agriculture

HONOLULU — Wearing camouflage fatigues and heavy combat boots, Aaron Works, Kari Bogner and Tehere Gibbs march through the quiet, upscale Honolulu neighborhood of Mililani Mauka. It is a hot Monday in July, and the sun throws hard shadows on the manicured lawns. The trio is heading for a densely forested gulch just beyond a row of houses, where they will spend several hours laying down little plastic vials marked with miniature red flags and smeared with peanut butter meant to entice tiny ginger invaders.

Though the combat gear is just their standard field-work uniform, the three really are at war: They are working to eradicate one of the island state’s most dreaded and tiniest enemies, Wasmannia auropunctata, also known as the little fire ant for its diminutive size and fiery sting.

Originally from South America, the little fire ant ranks among the world’s 100 worst invasive species due to the ease with which it travels and the threat it poses to human and animal health, tourism, agriculture, horticulture and tropical ecosystems. Not only does its sting leave humans with angry, itchy welts for days, it is also known to blind mammals; attack ground nesting seabirds, small lizards and turtles; eliminate many other species of invertebrates and spiders in its range; and promote the growth of debilitating plant pests such as scales and aphids.

Over the past three decades, little fire ants have spread throughout the Pacific region and have badly infested parts of Tahiti, Papua New Guinea, northern Australia and the Galápagos Islands. Easily transported by human commerce, they are capable of stowing away in almost anything — cargo, baggage, building materials, cars, potted plants and produce. Wasmannia auropunctata is just one of roughly 40 invasive species that afflict the Hawaii islands; the onslaught of invasive species in the island state contributes to more endangered species per square mile here than anywhere else in the world. But the little fire ant has an impact disproportionate to its size. 

‘Pruning the trees, picking the fruit, becomes really difficult. The workers get stung, hundreds of stings a day.’

Casper Vanderwoude

manager, Hawaii Ant Lab

If Hawaii doesn’t step up its efforts to combat the ants, according to University of Hawaii estimates, over the next 10 years, individuals and businesses on the Big Island will have to bear losses of $140 million, spend $1.2 billion on mitigation and treatment and suffer 390 million stings.

“It doesn’t just affect one segment of society; it affects all segments of society,” said Casper Vanderwoude, the ant man of Hawaii. He runs the Hawaii Ant Lab in Hilo, on the Big Island, which is dedicated to eradicating little fire ants. He gives monthly “ant-killing 101” workshops that are habitually oversubscribed, and he taught Works, Bogner and Gibbs everything they know about tracking the critters. Vanderwoude estimates that around a third of the houses in Hilo are infested.

Residents have complained of stings from ants in their couches, beds and kitchens. Perhaps worst of all for Hawaii’s economy, little fire ants threaten to spoil this tropical paradise for tourists, who account for close to a quarter of the island state’s economy. In recent months, visitors at a number of beaches have reported getting stung by ants falling out of trees and swarming under them in the grass. One beach park has been shuttered for surveying and treatment.

The ants have already hurt agricultural and horticultural businesses. “Pruning the trees, picking the fruit, becomes really difficult,” said Vanderwoude. “The workers get stung, hundreds of stings a day — and infested product can’t be exported because it’s a quarantine pest.” Some Hawaiian farmers have had trouble hanging on to workers who pick fruit and flowers. A few have even abandoned badly infested farms. And both farmers and nursery owners have had ant-infested product rejected and sent back by inspectors from the mainland.

“Everyone is having a hard time killing them,” said one tropical fruit-farmer with a nine-acre organic farm on the eastern coast of the Big Island as she stood surveying a swarm of the tiny ginger insects under a dry leaf on a banana tree. She didn’t want to be named for fear of hurting her sales. Though the farmer has been treating the single infested acre every four to six weeks with a special gel bait concocted by Vanderwoude, the ants have not yet retreated. She and her husband wear protective clothing, but get stung several times a day. Ants have swarmed a few of her beehives, and her cows won’t go to pasture in the infested acre. She pointed out the ghostly film over the eyes of her border collies, working dogs. Many residents and farmers in this part of the Big Island have watched their pets go blind, their corneas slowly clouding over, which scientists have found to be highly correlated with the presence of little fire ants. “I’m not the one who brought them here,” she said. “Why is the farmer having to foot the bill?” 

‘Where it’s infested, these ants just tend to fall out of the trees. It’s a continual rain of ants on people and animals.’


Banana trees in Hawaii, where little fire ants like to nest.
Age fotostock / Alamy

Measuring just one-sixteenth of an inch, about the thickness of a penny, the little fire ant is little indeed, and this is part of the problem. Entire colonies can hide in the folds of a single leaf or a macadamia-nut shell. This means they can easily go undetected as they hitch rides from one place to another, even as their colonies grow to unmanageable proportions. Unlike most other pest ants, they also nest in trees, and each colony has multiple queens, allowing the ants to build supercolonies that span thousands of acres on the ground and into tree canopies, with up to 80 million ants per acre. Because they like wet, shady habitats, they are especially suited to Hawaii’s rainforests.

“Where it’s infested, these ants just tend to fall out of the trees. It’s a continual rain of ants on people and animals,” said Vanderwoude, “because they’re arboreal, but they’re not very good at staying up there.” Brush up against the trunk, whack at the tree with a machete or shake the branches when picking fruit or coffee and one can be showered with hundreds of ants. They won’t sting unless threatened, but are easily caught in shirts and waistbands. And when one ant bites, it emits an alarm pheromone, which causes other little fire ants in the vicinity to bite in unison.

The presence of little fire ants was first reported in Hawaii in 1999, in the rainy, agricultural southeastern corner of the Big Island. Scientists suspect the ants came over from Florida in potted plants. Despite early efforts by the state Department of Agriculture to contain them, they are now so widespread on the Big Island that most conservationists say they will be impossible to eradicate. By contrast, smaller infestations on Kauai and Maui have so far been kept in check, and no ants had been reported on Oahu — until December.

The Mililani Mauka infestation, which Works, Bogner and Gibbs are mapping, came to light in June and was the second to be reported on Oahu. The first was discovered just a few days before Christmas last year and traced back to the Honolulu neighborhood of Waimanalo, where a number of plant nurseries are located. The ants had apparently hitched a ride from the Big Island, lodging themselves in the porous trunks of native hapu'u ferns, according to entomologists at the Hawaii Department of Agriculture. The ferns are often used as nursery logs for orchids and other plants, and more than 1,000 had been shipped to nurseries in Oahu and Maui. Though a treatment program was immediately launched, the fear is that the unrecovered hapu'u logs — the agriculture department was able to recover about 600 — will spread the ants all over Oahu.

The ant scare, coupled with near-daily stories in the media, led legislators to quickly roll out several bills targeted at controlling little fire ants and invasive species in general. One would have established biosecurity facilities at Hawaii’s airports and ports; another would have fined individuals found responsible for moving the ants from one island to another. Ultimately, none of the proposed legislation passed, in part due to pressure from the farm and nursery industries. But the statewide Hawaii Invasive Species Council got a record $5 million in appropriations funding for its upcoming budget, more than five times what it received last year.

A lab bait test for Hawaii's little fire ants.
Kristen French

Conservationists say invasive species such as the little fire ants will continue to spread without better regulation similar to what island nations like New Zealand and Australia have put in place. New Zealand, for instance, goes so far as to require inspection and treatment of mud on all sports gear, camping equipment and hiking boots entering the country. Meanwhile the U.S. Department of Agriculture requires luggage bound from Hawaii to the mainland to be X-rayed, which can catch undeclared agricultural goods; yet Hawaii, which is much more vulnerable to invasive species, does not require similar inspections of luggage coming into the state. Here, agricultural enterprises aren’t even required to register with regulatory agencies, which makes it harder to control and communicate with them when there is an outbreak.

Further, a nursery can ship anything interisland without inspection by the Department of Agriculture as long as the nursery is certified — but the certification process only happens a few times a year and applies to just a few pests; typically, inspectors only test the designated areas. The Hawaii Department of Agriculture doesn’t have the authority to require inspection of any nonpropagative material — a category that includes everything from hapu'u logs, tropical fruits, vegetables and cut flowers to cars, boats and building materials — all perfect hiding places for a little fire ant.

Rob Curtiss, an entomologist with the plant pest control branch of the Hawaii Department of Agriculture and the “incident commander” for the state’s interagency program to control the little fire ant, said the department is working to draft voluntary compliance agreements for businesses that ship interisland. But those rules will do nothing to prevent the continued spread of little fire ants around the Big Island, as happened a few years ago when the ants moved from the rainy eastern side to the sunnier, more touristy western side, infesting coffee farms.

‘You tend to want to rip your clothes off, because it hurts that much.’

Kim Johnson

coffee grower

Award-winning coffee farmer Kim Johnson says her Honaunau farm, on the western side of the Big Island, was the first in Hawaii to get little fire ants. Because she sells her coffee preroasted, her customers don’t have to worry about receiving contaminated product, she says. Johnson first noticed the invaders during the early harvest in October 2012. It was the middle of the day, and when she went out to her orchard to pick the coffee, ants rained down on her in a sheet. She was severely bitten on her chest and neck; the bites remained swollen like boils for two weeks afterward and have left her skin permanently discolored. At first she thought she had been stung by wasps. “You tend to want to rip your clothes off because it hurts that much,” she remembered. But then she shook out her clothes in the sink, saw the ants and sent them in for testing to the Hawaii Ant Lab.

Johnson said she knows other coffee farmers who have little fire ants but don’t want to tell anyone, because the presence of little fire ants on a property being sold must be disclosed to interested buyers until it can be verified that there have been no ants for three years. “As a commercial property, that cuts the value immensely, by a quarter or one-third,” she said.

Johnson believes the ants crossed into her farm from an abandoned property next door that was full of old junk, and she has spent the past two years treating the one-acre area on her own farm where the ants were found and another infested acre on the property next door every five weeks. She used Vanderwoude’s gel bait made with Tango, a pesticide that contains an insect-growth regulator — which meant she lost her organic status. She didn’t try to harvest or prune the area — a third of her farm — at all during that time, which resulted in significant lost income. Finally, in May of this year, testing revealed no ants. But she’s not taking anything for granted. “I’m not sure yet that I’m clean,” she said. “I’m going to keep on treating.” 

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