Click to enlarge the photos and really see the amazing patterns, especially in the one exposed wing.
And a little video, to show the brilliant orange, if just for a second, under its wings:
I'll try to find out what it is. Reminds of an Oregon bug we used to call "f*ck bugs," because you'd so often see two of them flying around in flagrante. (Those ones are box elder bugs. That ought to help me find them.)
Update: This is very fun. Because they look like box elders, I googled the genus of box elders, Boisea, with "Australia." I got nothing, in both "web" and "images". So I moved back on the taxonomical ladder, to the family, Rhopalidae. I got this:
You can see especially in the bug on the right the similarities in the triangular wing cover patterns, and especially in the big wing sticking out—clearly just one wing visible, giving it a one-sided look—just like our bug. So I think I'm on the right track.
Update II: Closer...
Update III: Almost there:
That's it! It's the Eucalytus Tip Bug, Amorbus alternatus. Success!
They have lots of other names, apparently, including squash bugs, and come in a variety of colors.
And check out this sentence:
Scentless Plantbugs in Family Rhopalidae are closely related with Coreidae but lacking well-developed scent glands.
Coreidae is the family of our bug here, and it's closely related to the Rhopalidae family I used to search. So my internet sleuthing technique worked!