|red imported fire ant (Solenopsis invicta) by USDA APHIS PPQ Archive, USDA APHIS PPQ, Bugwood.org|
Part of the reason may be their ingenious excavation techniques. When presented with large-grained soil, they will grab one piece at a time and move them out of the tunnels. When encountering finer soil, they with grab and compress multiple grains together and move the compact piece our of the tunnel. Having techniques in place to address different soil types has allowed them to invade across many substrates.
Source Article: Invasive ants are extreme excavators
More images: red imported fire ant