There are no ants native to Hawaii, so whenever a researcher sees an ant, it’s an invader. While scouting for the long-established Argentine ant along Waipoli Road in 2009, University of Hawaii entomologist Paul Krushelnycky discovered an extensive field of odorous house ants.
It was a surprise, because although these ants are native to much of North America, they hadn’t been found in Hawaii before. In a research paper published in Myrmecological News (online in September, scheduled for print early next year; www.myrmecologicalnews.
org), Krushelnycky and Grzesiek Buczkowski, an entomologist at Purdue University, wonder whether it may signal a new wave of ant expansion.
Over the past century, tropical ants, including fire ants, have swept the world, but temperate zone ants have not been as adventurous.
The mysterious colony of odorous house ants in remote Waipoli raises more questions than it answers.
And while odorous house ants do not bite people or chomp on buildings, they could pose an additional threat to native insects by outcompeting them.
Krushelnycky said he is concerned because invaders have already made huge inroads at lower elevations, and the odorous house ant (Tapinoma sessile), which lives as far north as Canada, might find a home in the higher elevations of Haleakala National Park, where tropical ants find it too cold.
Odorous house ants have already found a happy home in Kula. In North America, they are inconspicuous, living in small colonies in leaf litter, but when they move to the city, or to warm Maui, they learn different habits.
The Waipoli infestation covers a huge area, about half a mile across at least, and it may be a supercolony. DNA testing will be needed to confirm that, but ant fights suggest it.
In the wild, odorous house ant colonies are small, with a single queen. In warm buildings at Purdue University in Indiana, Buczkowski said, they have formed supercolonies with 25,000 queens and 5 million workers.
By putting workers from different nests in a glass vial, Krushelnycky and Buczkowski observed whether they made antagonistic movements or got along quietly.
Ordinarily, ants from two nests would not get along. In Kula, the ants were peaceable, although less so the farther apart any two nests were, suggesting that all are closely related.
That does not mean the ants are gathered densely together. The nests are widely dispersed, and the ants share their territory with seven other species, including the Argentine ant and the big-headed ant.
This raises questions for the entomologists, because past work has found odorous house ants to be outcompeted by Argentine and big-headed ants. They seem to be holding their own in Kula, though.
Cas Vanderwoude, who devised a novel bait that allowed eradication of a colony of little fire ants in Waihee before they could irrevocably establish themselves, wrote in an email: “It’s really hard to predict what a new species will do once it arrives in a different environment. . . . Certainly Paul’s research on Argentine ants in midelevation parts of Maui show there could be cause for concern” with odorous ants as well.
“The issue here is that we have a very narrow window of opportunity to eradicate something once it is discovered. Without certainty about potential impacts, it is difficult to present an economic case for funding.”
Funding is scarce now, anyhow, and nobody knows how long the odorous ants have been at Waipoli, according to the researchers.
Because they already cover such a big area, Krushelnycky said he is doubtful they could be eliminated.
The little fire ant colony that was destroyed was in a much smaller area.
There is a difference of opinion about what odor odorous house ants emit.
They come from a family notable for the smelly defensive chemicals they make. Some think their smell is like coconut, although Krushelnycky said that, at best, it smells like rotting coconut to him.
Buczkowski described it to a Purdue journalist as reminiscent of pina colada.
Vanderwoude, who works in the Pacific Cooperative Studies Unit at the University of Hawaii-Hilo and with the state Department of Agriculture, participated in the Waipoli surveys, but he said he doesn’t know why Tapinoma smells as it does.
Many ants have distinctive smells (and tastes; Vanderwoude sometimes tastes ants). “There is another species in Australia that smells like mint-chocolate!” Vanderwoude wrote. But, “some ant species taste vile, so choose carefully!”
* Harry Eagar can be reached at firstname.lastname@example.org.