What’s Eating Your Empanadas? It Could Be An Argentine Ant

The Argentine ant (

Linepithema humile

) is by itself unremarkable: it is barely three millimeters in length, a poor vector for disease and incapable of biting or stinging. It is, however, taking over the world.The largest known megacolony of Argentine ants stretches more than 6,000 kilometers—that’s 3,700 miles—along the Mediterranean coast of Europe. Claremont sits at the heart of the world’s second biggest megacolony, which has made its way up the California coast for more than 560 miles with no signs of slowing.The ants are found on six continents—excluding, of course, Antarctica—and have been unintentionally introduced to some the earth’s most isolated archipelagoes. Wherever we are, they are. They have ravaged woodlands in California, subalpine shrub lands in Hawaii, and oak forests in Portugal. They have killed off army ants ten times their size, taken over entire bee colonies, and threatened insect-pollinated plant populations. They are a nuisance to millions of people worldwide who have had to deal with overwhelming infestations, including here in Claremont.Walker dormitory resident Sasha Bartashnik PO ’10 had a major run-in with the Argentine ants the moment she walked into her dorm in late August. Apparently entering from a hole in her ceiling, a thick line of ants wound across her room and onto her bed. For what reason, she has no idea. “There are too many,” she said. “I have ant paranoia.”All this from an insect that is, even by entomological standards, not at all noteworthy. The Argentine ant is a small, medium-brown omnivorous species with a shiny, hairless body surface. As its name suggests, the ant is native to Argentina and favors temperate weather, though it has learned to exploit human comforts in colder climes. It is monomorphic—that is, all members of the species are physically identical, regardless of their specialized role in the colony—and have very low genetic diversity.What they lack in individual charm, however, they make up for with a little help from their friends, and they have billions of them. The Argentine ant is one of the few known species that cooperate across colonies of the same species. Whereas other ant species will fight to defend their territory against invasion by other colonies, the Argentine ant makes no such distinction, which is why their colonies have grown so large. The North American ant population most likely radiated out of a single ant colony—or a single pregnant queen—that arrived at a Louisiana port in a shipment of coffee from South America. They are, essentially, one large family. A recent study at the University of Tokyo found that ants taken from Spain got along perfectly fine with their Japanese and Californian counterparts. This interconnection between colonies has driven a massive radiation of the species with structures, like the Mediterranean megacolony, that rival human society.It would be poignant, if it were not so obnoxious, and so hazardous. The ants were listed as one of the most invasive species in the world by the Invasive Species Specialist Group, the global authority on such matters. They have been charged with critically endangering native insect populations, like the harvester ant in Southern California, which has had major impacts on insectivores like the threatened horned lizard. In Hawaii, the ants have ravaged endemic arthropod populations and contributed to the decline of plant-life found nowhere else in the world.“They’re not dangerous to humans, but they’re ecologically dangerous,” said Professor of Biology Jonathan Wright. “They’re vicious to other species and highly invasive.”Humans have also played a pivotal role in the success of the Argentine ant, especially over the course of the past few decades. We unwittingly ship millions of ants around the globe in freight and agricultural products, extending their geographic reach and providing genetic diversity. The ants have also been very successful at taking advantage of urban sprawl, which has opened millions of acres of new habitat in areas that were uninhabitable without human amenities like heat and running water. Not to mention the food we provide.For these ants, feeding is simple. A few worker ants will go out in search of food, and leave a feeding-pheromone in their wake, which can be smelled from miles away. The ants smell the pheromone, then march in orderly lines to feed by the millions, sometimes navigating through electrical sockets, ceiling panels, and holes in the stucco.There is no wonder why ants feel at home on campus. The worst infestations are, unsurprisingly, set off by food left out in the open. Food waste in hall trash cans, unwashed takeout containers, and even cups of water can draw the ants out of the woodwork and into your living space.Attracting the ants is easy; getting rid of them is another story. Pomona College has been combating the ant problem with an aggressive pest control regimen. Maintenance and grounds workers spray hot spots with pesticide over the summer and trim down foliage near buildings that could serve as bridges for the ants. The perimeters of buildings are also sprayed with pesticides each month, and students can have a maintenance worker spread nontoxic—but highly effective—ant-killing powder in affected dorm rooms. Ant traps, which encourage the workers to take tainted bait back into their nests, have also proven effective at mitigating the problem. Even those measures, however, have not been enough to stem the influx of Argentine ant invasions in the past decade.“We use everything that we can,” said Judith Brown, director of maintenance at Pomona. “It’s a real battle.”Researchers at the University of California at Irvine are currently working on a solution that would essentially turn the amicable colonies against each other. Scientists have found a way to alter the chemicals that ants carry with them on their exoskeletons that identifies them with a certain colony. Make an ant think that its nest-mate is from a rival colony, and they will literally tear them limb from limb. It is chemical warfare on a tiny scale, but it is no less sinister. Whether or not you want the ants poking around, it is a definite blow to one of the animal kingdom’s greatest testaments to teamwork.

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