Officials in the western Japanese port city of Kobe say about 100 more fire ants have been found in a container storage space.
The highly poisonous ants are originally from South America. Their sting can cause anaphylactic shock, which may result in death.
Hundreds of them were found on May 26th in a container that was unloaded at Kobe Port and transported to Amagasaki, east of Kobe. It was the first time the ants were found in Japan.
The container came from Guangdong Province in China.
An emergency investigation by city officials on Friday found similar ants in Kobe Port, where the container was kept for 5 days. They were confirmed to be fire ants on Sunday.
About 100 of them were found in cracks in asphalt pavements and other places about 30 meters from where the container was kept.
City officials say they will continue to investigate the port and places where the container was transported. They are calling on people to report to the city office if they find unfamiliar ants near the port.
In the United States, it is estimated that more than 100 people die annually after being stung by fire ants.
The ants have spread to China, Taiwan and other parts of Asia via cargo ships and other routes over the past 10 years.