Queensland cane toad, poisonous toad introduced as insect pest control, totally out of control and killing anything that eats it
Pattersons curse introduced by bitch patterson (so im told) as a pretty wild flower, totally invasive and we spend fucken 100s of million killing the shit every year to plant crops
European carp, intoduced as a game fish, has decimated the river systems in australia, wiping native stocks and they are bottom feeder stirring up the slime in the water all the time
The wild pig is really messing up Australia's wildlife. Australia has some of the tightest imports laws on the planet. It's always funny to watch Asians ask shit like, "Why can't I bring in this tea that crawling with bugs?"