We have only seen this species over one period of a few weeks when one or more of them was seen on a dead Sugar Gum. This had numerous holes about 5mm diameter, and the wasp was seen going in and out of 3 holes in quick succession, obviously hunting for something.
Classification
from Australian Faunal Directory
Order Hymenoptera - Wasps, Ants, Bees and Sawflies, 12202 named species in Australia
Family Crabronidae - Sand Wasps and Others, 805 named species in Australia
Genus Williamsita
Species ?