@WendyEM Myrmecia gulosa is a good suggestion, but almost all images on the Atlas of Living Australia shown the colour of the mandibles of Myrmecia gulosa as yellow or distinctly lighter than the head, and the gaster (abdomen) bicoloured, with the front part of the gaster red and the back part black. The ant also looks a lot like Myrmecia simillima, but I'm not sure enough to ID to species level. Cheers, Jon