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

Japan’s climate is a strike zone.

The natural expansion range of Argentine ants is only about 50 to 150 meters per year, but most of their spread to distant areas is caused by human activities, such as being transported by cars. Unfortunately, Japan’s climate falls right within their ideal range. Their expansion shows no signs of slowing down, and areas like Hiroshima and Yamaguchi, which previously had spotty distributions, have now become a continuous belt of infestation.

Currently, the pesticide Mr. Sunamura is involved in developing is being sold to local governments. Since the Argentine ants haven’t spread everywhere in Japan yet, regional eradication is essential. Although it’s not available in stores yet, what should you do if Argentine ants invade your home?

“In the U.S., research has shown that a component found in aromatic cedar (pencil cedar) can repel Argentine ants. It’s used in chip form to cover gardens, but the effect seems to wear off over time, lasting perhaps one season.

Also, since they tend to build nests under flowerpots or stones, it’s a good idea to avoid placing such items around. Sealing cracks in exterior concrete walls can help prevent them from entering the house.”

To differentiate them from common ants, if you notice a sudden increase in small, fast-moving ants, they may be Argentine ants. Unlike regular ants, they don’t march in single file but spread out in a wide formation, attacking like a carpet.

Mr. Sunamura is so fascinated by Argentine ants that he travels across five continents researching their extermination methods, taking countless photos of trash bins and the walls of people’s homes, sometimes even getting questioned by authorities (though he always gets permission to photograph buildings).

Despite his research on extermination, you can sense a certain fondness for the ants in his words. What kind of future does he envision for them?

“While it’s necessary to control them, I don’t want them to go extinct. Ideally, they’d thrive in their native habitat.

In places like California or the Mediterranean coast of Europe, for example, it seems almost impossible to eradicate them. In such areas, I hope they don’t disrupt the ecosystem, but instead find a way to coexist. Argentine ants were unintentionally transported and are now trying to survive in their new environments, so it might be our responsibility as humans to find a way to coexist with them.”

▼Eiriki Sunamura (Eiriki Sunamura)
Entomologist and photographic artist. He earned his PhD from the University of Tokyo, researching the ecology and control of the Argentine ant (recipient of the University of Tokyo President’s Award). After working in insecticide research and development at Sumitomo Chemical, he is currently engaged in pest control research at the Forestry and Forest Products Research Institute (on secondment from the Forestry Agency). His work focuses on recording the ecology and creating artistic works using invasive species such as ants and longhorn beetles. He is the recipient of the Asahi Camera Award at the Yoshiaki Tabuchi Photography Competition. Sunamura is a member of the Japan Society of Scientific Photography and a part-time lecturer at the University of Tokyo (insect phylogeny and taxonomy). He is the co-author of books such as The Argentine Ant: The Most Invasive Species in History (University of Tokyo Press) and The Society of Ants: The Big Wisdom of Small Insects (Tokai University Press).

Click here to purchase Sunamura’s book, “Survival Strategies of Ants that Rule the World.