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Flower Wasp - Tiphiidae - Hemithynnus sp.
Wasps in the Tiphiidae family are generally known as Flower Wasps as the adults feed on the nectar of various flowers. It is a large family that is represented in Australia by 3 sub-families, two of which both the male and female wasps have wings, but in the third Thynninae, the female is wingless and is carried about or otherwise feed by the much larger winged male.
The male thynnine wasps are attracted to the females when she releases a pheromone to indicate she is ready to mate. It is interesting to note that many plants, particularly orchids mimic this pheromone to attract the male wasp, who inadvertently pollinates them when they grasp the labellum, which they think is the female. However most of these wasps would be much smaller than this species (probably a Hemithynnus sp.) that is over 3 cm (11/4”) in length (excluding antennae), so a little large for most orchid flowers. The wingless female above (which may not be the same species) is about a third the size of the male.
These wasps are parasitic on the larvae of burrowing scarab beetles, whereby after mating the wingless female digs into the soil to locate them and will then lay at least one egg on each. They must encounter a number, as they are reasonably common in the Esperance (near coastal) sandy heath from November to January.