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

 

“It seems that in their native habitat, they originally lived along riverbanks. Since floods often occurred there, if a single queen tried to establish a new nest far away, there was a high chance she would be swept away and die before she could succeed. So, they evolved to think, ‘Instead of that, it’s better to quickly spread the nests nearby and be well-prepared. If we spread out to a certain extent, we can avoid total annihilation, and in the case of a disaster, everyone can evacuate to the nest that sustained the least damage.'”

I see. Hearing the story, it sounds almost like a cheerful, cooperative community. But the situation is far more serious than to allow any fondness or attachment toward them.

Argentine ant infestation causes real estate values to drop

The first Argentine ant in Japan was discovered in 1993. By 2004, when Sunamura first learned about this ant in a university lecture, it had significantly increased in numbers in Iwakuni City, Yamaguchi Prefecture, causing problems for the residents.

“Compared to other insects, methods to exterminate Argentine ants had not yet been developed, and the issue was quite significant. I thought I could conduct some useful research on it, so I chose it as my study subject,” he explained.

So, what kinds of problems arise when this ant proliferates? Let’s summarize briefly:

Disruption of the Ecosystem: Native Ants Are Driven Out

In invaded areas, native ants are driven out, leaving only Argentine ants. In a survey conducted by Sunamura in Kobe City, there were 13 species of ants observed in areas where Argentine ants hadn’t yet invaded, but only two other species could occasionally be seen in invaded areas. The loss of native ants affects various organisms, including plants.

“They gang up, with five or six Argentine ants surrounding a single native ant, pulling at its legs and antennae like a scene from Gulliver’s Travels. Then they poison it or tear it apart.”

This impact on native species has been observed worldwide. In the U.S., lizards that primarily fed on native ants have drastically decreased. In Hawaii and South Africa, notable ripple effects and concerns for other animals and plants, such as the Cyanea plant and the Fynbos ecosystem, have also been reported.

Agricultural Damage: Ant Parts Found in Homemade Jam

Argentine ants love the “honeydew” secreted by aphids and scale insects. In their pursuit of honeydew, they protect these pests from their natural predators, causing their numbers to increase and spread diseases in crops, leading to damage. When nests are built in fields, root crops like carrots can be gnawed on, leading to deformities such as split roots.

“I’ve also seen cases where they end up inside the fruit of figs. I was once treated to some homemade fig jam in an invaded area, and upon closer inspection, I could see fragments of Argentine ant heads and legs in the jam.”

There have also been reports of the ants attacking beehives and hindering the collection of nectar, negatively impacting beekeeping.

Damage to Living Environments: Overtaking Cockroaches as the No. 1 Pest

There are numerous cases of Argentine ants invading homes. Due to their sheer numbers—five to ten times more than native species, according to Sunamura’s estimate—they can’t be contained just in underground nests and end up invading houses. In addition to the nuisance of swarming food and offerings, disturbing sleep, and biting pets, they also cause damage to electrical equipment.

“It seems they crawl into areas where they shouldn’t be, get electrocuted, and their dead bodies cause short circuits. The damage is extensive, leading to air conditioner or intercom malfunctions, flickering lights, and other breakdowns.”

In the U.S., Argentine ant invasions have led to decreased property values in some areas, even forcing people to move out.

“In California, they’re considered the No. 1 pest, surpassing cockroaches. The best-selling insecticide spray there features ants prominently in its illustrations. The same is true in South Africa.”