Australia’s largest bee is the Carpenter Bee, Xylocopa species. Females are black-and-gold monsters which are sometimes thought of as ‘Bumblebees’, although that name really belongs to an introduced species which has made itself at home in our southern states.
Carpenter Bees are solitary, like many other native bees, and they make nests by hollowing out chambers in soft wood. I have known them to use dead branches of our frangipani trees and, more recently, a dead branch of a small native tree (a ti-tree, if I remember correctly, but it has been dead for so long that I’m no longer sure). The nest holes are quite distinctive: a round hole the size of the tip of my little finger, as neat as anything I could do with a drill. The female provisions the cell with pollen as food for her offspring.
There’s a lot more about these bees at aussiebee.com, with photos which I must say are far better than mine. The best shot of all is the second photo on this page showing buzz pollination in action. Amazing!