Originally posted by photolady95 They look like the assassin bug nymphs we have here but ours are bright red which also gather like yours do, Arjay.
The bugs in the images posted by Arjay Bee are not assassin bugs, but they are in the same group = Heteroptera* or "true bugs." The unmistakable identifying features are the half-hardened anterior wing and the diamond-shaped pattern of the veined wings exposed at the back end of an adult at about 7 o'clock in the second image in particular. I cannot identify any but a handful of about 3,800 species in the USA, much less those in Australia..
*Heteroptera includes two groups of insects that were formerly separate = Homoptera which includes leafhoppers such as in the second image posted by noelcmn just above, and Hemiptera = "half wing" or "partial wing" bugs, a very diversified group that includes the assassin bugs as well as those pictured by Arjar Bee.