A giant colony of ants has been discovered spanning 100km across Melbourne.

The supercolony of Argentine ants stretches from Taylors Lakes, north-west of Melbourne, to Sorrento, south of the city.

The ants have also been spotted in Altona, in the western suburbs and in Blackburn, in Melbourne's east.

Monash University researcher Elissa Suhr, who discovered the supercolony, said they may look like harmless household pests, but the ants posed a significant risk to Melbourne's biodiversity.

They had the potential to displace native plants and animals, she said.