Its a Blue Flower Wasp Discolia soror which lives on nectar, and apparently layes its egg on scarab beetle grubs which are buried deep in the soil.
From what I've read about it these predators are one of those bugs you DO want in your garden as along with pollinating native plants, they prey on scarab beetle larvae which are largely responsible for defoliating mature eucalyptus's . This one is a male as the females are wingless, and live their lives crawling around the garden, whereas the males zoom around the place using their large luminous blue wings.Feeding on leptospermum and other native nectar its thought they also feed off the sugar solutions secreted by aphids and scale insects. That would explain this guy hanging around the roses.
Unfortunately the photos I got of it aren't in perfect focus, but its about 30cm long with quite a large wing span, sadly I think it may have been on its last legs.
|A more in-focus pic of this wasp which I found here: http://www.whatsthatbug.com|
Scarab beetles, also known as Christmas beetles are abundant around here over summer so I hope this Blue wasp managed to find a mate and we will see more of them, as I do love our flowering gum and dont particularly want it to be defoliated.