Tasmanian authorities are investigating after a single red imported fire ant was detected at an Australia Post parcel centre in the state's south.
The ants are one of the worst invasive species to reach Australia, with the potential to inflict painful bites on people, pets and livestock.
The package has been traced and additional surveillance and trapping operations have been put in place.
"This border interception does not mean there has been an incursion into the state, and Tasmania remains free from RIFA," Biosecurity Tasmania said in a statement.
"This detection was made as part of business-as-usual surveillance operations at mail centres across the state.
"Australia Post staff have been provided additional information on detecting RIFA specifically in parcel mail."
Last week, invasive red fire ants were discovered in Wardell, south of Ballina, New South Wales, in the most-southern discovery of the destructive pest yet.
Originating from South America, the species was first detected in Australia in 2001.