Fighting for an island

Invasive Little Fire Ants have already taken over the Big Island, and now Maui is trying to save itself from a similar fate

April 8, 2020
Tiny ants crawl across a jungle vine as a helicopter flies overhead
In an ongoing fight to halt the ants, a specially-modified helicopter is the latest weapon. [CKSegarra | CC-BY-4.0]

Deep in the verdant jungle of Hawaii’s Maui island, isolated colonies of millimeter-sized ants are thriving. Countless worker ants are crawling about on the broad, heart-shaped leaves of hibiscus trees, wrangling aphids to provide a source of food for the single queen ant. Without predators, the Little Fire Ants live in a paradise far removed from Central and South America, their species’ natural home. But the unmistakable sound of helicopter blades beating through the tropical air is a bad omen — a terror from above is about to rain down on the impassable foliage harboring the ants. If the plan works, the queen will be sterilized and the colony will collapse. And Maui’s locals will be one step closer to preserving their paradise from an island-wide invasion — a fate the neighboring Big Island of Hawaii has already suffered.

As a warm, forested tropical archipelago, Hawaii has a long list of invasive species that have shown up and threatened local ecosystems over the years. From swarms of Coqui frogs to meandering mongeese, Hawaiians have seen their fair share of invasives, but Little Fire Ants are unique. With bodies so tiny they’re hard to see, and a sting so painful they have affected yard work, surfing, and even labor relations, some locals and committees on Maui and Kauai are willing to go to extreme lengths to stop their spread.

A Little Fire Ant’s sting sort of feels like a jellyfish sting, says Brooke Mahnken, who works with the Maui Invasive Species Committee, which recently took the battle to the skies via helicopter. “The problem with the Little Fire Ants is that generally when it happens, you’re covered in ‘em and they all start stinging at the same time,” he said during a Skype interview.

The ants were first spotted on the Big Island in 1999, but their lineage traces back to Florida, and the Floridian ants came from Cuba, according to a genetic study. A queen ant, necessary for reproduction and the development of a colony, probably came to Hawaii in a shipment of plants, according to a 2015 study. The same research reveals that, fifteen years after they were first detected, the ants had quickly invaded over 4,000 locations on the Big Island — an impressive feat for ants the size of a pinhead.

Of course, they had some help from humans. Riding in bags of compost, on garden tools, or clinging to plants shipped from nurseries, the ants spread from yard to yard across the Big Island. Despite early efforts to control the invasion, they continued to increase in number and range. On Hawaii, it’s humans that are really feeling the pain. Recently, the ants have changed fundamental aspects of life there. Farm workers, home gardeners, hikers, and even surfers are getting stung.

“I grew up in Hilo and I remember climbing trees and just rolling around in the grass,” says Kawehi Lopez, a twenty five year old surfer and native Hawaiian, “we never got scared about fire ants.” But, by 2016, Hilo was infested. The ants were in the locals’ backyards, climbing on their trees. Now, the ants have reached Honoliʻi, a popular Hilo surf spot, where a river spills into the Pacific off of Hawaii’s east coast.

“When we have big rains and big winds, the ants — they aren’t really great at holding on,” Lopez says, so the ants get blown into the river and carried out to sea. “One of the spots that I like to surf is right where that river water is coming out,” Lopez says, so she’s been stung while out on her surfboard. 

“Yeah, I actually pulled one off,” Lopez says. “It was right by my armpit.” And she’s not the only one getting bitten in the water. She put up a post on her Instagram to see if other surfers had similar experiences. Several had felt the uncomfortable sting.

Little Fire Ants sting with their abdomen. A single sting is painful, but bearable. Multiple stings are a different story. They’re enough to make outdoor work impossible. Because the ants tend to colonize trees in Hawaii — and because the ants don’t have much grip — Hawaiian fruit harvesters are particularly prone to being stung by multiple ants. The stings have been so bad that for Hawaiian farms that rely on local pickers for work, the ants have exacerbated the current labor shortage on the Big Island.

“It’s actually caused our workers to say they don’t want to pick certain sections of the farm,” says Suzanne Shriner, co-manager of Lions Gate Farms on the Big Island, which produces coffee and macadamia nuts. Little Fire Ants showed up on the farm about two years ago, Shriner says. And during last year’s harvest, workers refused to pick Kona coffee from the infested section.

“When they do get bad and out of control, there’s very little we can do in the short run, which caused us to lose some of our crop on the tree because it just couldn’t get picked,” Shriner says. “The Little Fire Ant is just such an annoyance and a deterrence to your labor that it can actually mean the loss of your entire crop.”

“It’s really hard with coffee. We don’t really have any products we can use to knock them down right away,” Shriner says. “We only have the long term growth regulators, like Tango, which take several months to use.”

Tango is one of the brand-name insecticides commonly used to treat Little Fire Ants in Hawaii. According to Cas Vanderwoude, research manager of the Hawaii Ant Lab, Tango’s active ingredient, S-methoprene, is an insect-growth-regulating chemical that disrupts the hormones of the only ant in a Little Fire Ant colony that can reproduce: the queen. A popular application technique — mixing it into a runny paste and spraying it into trees with backpack sprayers — was developed by the Hawaii Ant Lab to combat the ants on the Big Island. Recently, people on Maui have been using it to try to prevent a full scale invasion.

“Now that is birth control for the queens,” says Brooke Mahnken. “It tricks the queens into thinking they’re too young to lay eggs,” he says. “As long as you continue to feed them that, they won’t lay eggs and eventually workers die of old age — in one to three months. And then the queens are not protected and fed and tended to by the workers. They’ll eventually die.” 

S-methoprene has been proven effective against ants and mosquitos, and it’s a relatively safe pesticide, according to a 1999 report. There is evidence that it can change honey bee foraging patterns, but research shows that it doesn’t pose much of a threat to plants, fish, birds, or humans, according to The United States Environmental Protection Agency’s pesticide fact sheet

“It’s very inert — low, low impact. We can use it on crops,” Mahnken explains, “it’s also the same stuff we’re using from the helicopter, because the helicopter is flying over waterways.”

The black and yellow-striped helicopter is specially modified to deliver over 300 gallons of S-methoprene-based ant bait per trip to the dense forest canopy of Maui’s east coast, where the ants have recently invaded.

Though Maui is separated from the Big Island by the 30-mile-wide Maui Channel, the Maui Invasive Species Committee was wary of the threat the ants posed if someone were to import Little Fire Ants, says Lissa Strohecker, who runs public education at MISC. So even before the ants were spotted on Maui, there was a community education program to caution locals to be on the lookout. Soon enough, they were spotted at an organic farm in 2009. Then, more ants were found on ferns that came from a local hardware store, explains Strohecker. Since then, there have been 10 additional sites where the ants have shown up on Maui. Some are in easy-to-reach suburban areas. Others are less accessible, like the site in the dense jungle of Nahiku.

Flying at about 11 miles per hour, the helicopter sweeps low, and a hose with five nozzles sprays the mixture onto the trees. The vegetation is just too dense, and the region too large — over 50 acres — to walk in and spray pesticide, Mahnken explains. “There’s a plant here. It’s called Hau,” he says. “It just creates this dense, huge, massive, twenty-feet high impenetrable thicket.” A helicopter may seem dramatic and expensive, but it’s really the only way to treat the ants in Nahiku. 

“For one application with the helicopter,” he says, “it’s about $10,000 worth of product [ant bait] alone.” So when you figure in the cost of the helicopter and personnel, treating 170 acres of land costs about $20,000 — about $120 per acre. Still, maybe it’s worth it — in 35 years, the ants could cause over $500 million in damages, according to one economic analysis.

The first heli-spray occurred in October, 2019, but spraying once isn’t enough, Mahnken says. To eradicate the ants, you have to spray every six weeks, for at least a year, he explains. Even then, it’s standard procedure to return to the site for several years after the last ant dies to make sure they’re gone for good.

To do this, workers at the Maui Invasive Species Committee place peanut butter-containing vials around the jungle. “Little Fire Ants really like peanut butter,” Mahnken explains. “We leave it out for about an hour, we come back, pick it up, take a GPS point, and we write a little number on that vial.” Then they take the vials back to a lab for analysis. “We have to identify these under a microscope,” he says. “You cannot be certain that they’re Little Fire Ants by your naked eye. Some people think that they can, but I don’t trust those people.”

When treatment works — once there are no Little Fire Ants in the vials — the crew will continue to survey the region for five years after the last ant was killed. Only after five years of ant-free surveys will they consider the site eradicated.

We “finally use the ‘e-word,’” Mahnken says. “But we don’t use it lightly.”

On the island of Maui, most of the invasions of Little Fire Ants are new, so it’s too early to know if the ants have been eradicated, Mahnken explains. It looks like all the hard work is keeping Maui’s invasion at bay for now.

But there are people that oppose the ant eradication work that the Maui Invasive Species Committee is doing. Some people are concerned about pesticides, says Lissa Strohecker. And there has even been a court case involving residents that didn’t want their property sprayed. Still, most people seem to support the efforts of the Maui Invasive Species Committee, Strohecker says.

Ultimately, total eradication of the ants from Hawaii is probably impossible, Mahnken adds. So just slowing down the spread of Little Fire Ants can be considered a success, and it’s something that many locals are willing to fight for.

“People on the Big Island voluntarily are treating their homes and their yards, and they’re going to be doing this forever — for perpetuity just so that they can be comfortable in their own homes,” Mahnken says. “And if that doesn’t convince you that you don’t want this ant, I don’t know what will.”

About the Author

Curtis Segarra

Curtis is a photographer and science journalist who focuses on health, Earth science, and ecology. Growing up in New Mexico, his life was centered around nature—hiking, biking, and exploring. When he wasn’t outdoors, he was reading (he loves travelogues). Later, while studying geology at Trinity University, he realized he could combine these passions by becoming a science journalist. Now, he uses his words and photos to help others see practical beauty in science.


1 Comment

Don says:

Good article.

Living in Hilo, I’ve been stung more times than I can count. Building some immunity to the stings is possible. Years ago, the stings would bother me for a day, even two. Now, it’s an hour, maybe two. Still, those are unpleasant hours.

One correction: the plural of mongoose is mongoose, not mongeese.

Leave a Reply

Your email address will not be published. Required fields are marked *


The Scienceline Newsletter

Sign up for regular updates.