The red fire ant, which can inflict a painful sting which causes blisters, and in rare cases prove fatal, has infested the Taiwanese capital Taipei.
By Chris Hogg
BBC Taiwan correspondent
Experts have warned it could take up to three years to eradicate the pest.
Taiwan is only the fourth place in the world the ant has spread to - it has already spread through New Zealand, Australia and the United States.
Now it has been confirmed that it has infested at least four large areas of Taiwan.
The red fire ant is vicious and aggressive. When it stings you, the sharp burning sensation can last for an hour and within four hours a white blister appears.
RED FIRE ANT
Originally from South America
Feeds on other insects, soft fruits and can attack small birds
Construct colonies on farmland
Stings cause blisters prone to infection, and sometimes anaphylactic shock
In recent days red fire anthills have been found in the centre of Taipei and the authorities have been spurred into action.
Taiwan's premier has urged people not to panic and advised them how to protect their children.
Agricultural experts suspect the red fire ants were brought into Taipei in the soil of potted plants or landscaping material. They warn it could take years to eradicate the pests.
They describe this as a war of attrition. The ants are blamed for losses of US$5bn in the United States each year and more than US$6.5bn in Australia.
Extra stocks of pesticide have been ordered by Taiwan's government. It hopes to contain the spread of the insects by the end of the year.
Complete eradication, which some doubt is even possible, is likely to take much longer.