I was walking through grass in Budderoo National Park and nearly stood on this mass of ants.
It seemed to be an eruption from out of the ground. Although the ants were densely packed, it was a living mass and I could see larvae or eggs being moved.
As it was quite a wet day I guessed that perhaps there had been water ingress into their nest causing this eruption but I have since learnt that this species commonly forms balls like this on warmer days.
An hour after encountering it, I returned to the same spot with my brother, Larry. The ants had disappeared.