Ranked No. 1 Pest in the U.S., Surpassing Cockroaches! The Alarming Spread of the Argentine Ant Across Japan

Once they build a nest they are extremely difficult to exterminate

They swarm in large numbers, destroying household electrical appliances, and turning offerings at family altars pitch black.

While the fire ant, designated an “Invasive Alien Species Requiring Urgent Action” two years ago, is well-known, the “Argentine ant,” which becomes extremely difficult to eradicate once it establishes a nest, is expanding its habitat across Japan.

Regarding the Argentine ant, which continues to breed on a global scale, we spoke with Entomologist and Photographer Eiriki Sunamura, who received the University of Tokyo President’s Award for his research on its ecology and control. He is currently engaged in pest control research at the Forestry and Forest Products Research Institute.

It took 170 years to conquer the five continents!

The Argentine ant (scientific name: Linepithema humile) does not have any particularly notable physical characteristics. It is small, about 2.5 millimeters long, and lacks venomous stingers or thorns. Its scientific name, when loosely translated into Japanese, means “insignificant ant.” It’s a rather pitiful name for such an unremarkable creature.

“In its native region of South America, there are many prominent ants, such as the Paraponera, which is large and equipped with a powerful venomous stinger; the Atta ants, which cut leaves to cultivate fungus and have distinct thorny bodies; and the fire ant, with its red body, venomous sting, and large ant mounds.

Compared to those, the Argentine ant, with its light brown color and lack of any special weaponry, was likely viewed as just an ordinary, unremarkable ant—a typical ‘mob character,’ so to speak,” says Eiriki Sunamura.

However, this mob character has been officially designated as an “Invasive Alien Species.” Eiriki Sunamura, who first learned about its existence during his university days and became more and more fascinated by this insignificant ant through his research, now calls the Argentine ant the “uncrowned king,” holding it in deep respect. But why is that?

“As the name suggests, its native habitat is in South America. However, research has revealed that descendants of a single colony (family) from its homeland have spread across Europe, North America, Asia, Australia, and other parts of the world, forming a global colony.

The expansion of this colony’s distribution began around 170 years ago. Since a new queen is born once a year, they have passed down their lineage through roughly 170 generations.”

Moreover, these ants have the ability to remember the origin of their colony. Each colony has a distinctive scent, which they use to identify members. When they encounter ants from a different colony, fierce fights break out, but when they meet ants from the same colony, they quickly become friendly.

“Although the descendants of this colony, found in Europe, America, Japan, and elsewhere, never meet in the wild, if they are brought together through importation, they can still recognize each other as part of the same colony.”

In general, ants have a reproductive season when new queens fly out from the nest to mate with winged ants from other colonies. The new queen then establishes a new nest, cutting ties with her original mother nest.

However, in the case of the Argentine ant, after mating, the new queen takes worker ants with her and quietly moves to a relatively nearby location, on foot. Since the blood relationship remains intact, there is no hostility with the mother nest, and they freely travel back and forth, cooperating with one another.

This splitting of nests is repeated over and over, eventually expanding into a massive extended family spread over several hundred meters to several kilometers. This marks the birth of a “supercolony.” Even if transported far away in a vehicle, they all remain part of the same supercolony, and in many continents, a single supercolony can stretch over several hundred to thousands of kilometers.

“People often imagine ants building well-structured nests with many separate chambers, and the queen’s room deep in the back, but Argentine ants are more casual. They just dig a quick tunnel-like structure and hang out there,” says Sunamura.

Because nest building is incredibly simple, they can quickly start foraging for food in their new location. Additionally, since they spend far less energy on territorial disputes, they can redirect that energy into reproduction.