These ants have turned up at a few different places around the garden, the seem to occupy a nest for a few months and then move on. They are semi aggressive and will swarm on you if you stand on their nest or get in their path. They don’t seem to bite though.
The photos are from the 3rd location I’ve seen them, and the first time I’ve seen them swarm in such a dense cluster. There was a lot of movement going on but it seemed ordered, like they were going about a task, some of the ants were carying white sacks around. I dropped a matchstick next to them to give a bit of scale in the photos and all hell broke loose. The ants swarmed so agressively that it made a sound, like a soft crunching. The matchstick was swamped. With all the new movement I got a better look deeper into the mound and could see many more white sacks underneath.
Whatever they were doing they had finished by the next day. The nest is still there and there are still lots of ants around, but nothing like the dense arrangement in the pictures.
I’ve got no idea what was going on, or what type of ants they are. I’ve been browsing CSIRO’s Ants Down Under page to try to identify them but it’s not proving to be an easy task. I don’t know what I’m looking for and the site is so painfully slow it’s not suitable to explore or browse about.
Nothing else to do but keep looking and post an update when I find out what these are.