Melittobia australica is a species of chalcid wasp from the family Eulophidae which is a gregarious ecto-parasitoid of acuealate Hymenoptera.

The "crawlers" remain within the host nest for the whole of their life cycle while the other morphs disperse as adults.

[2][3] Some authorities believe that it is indigenous to Australia but that human commercial activity has allowed it to spread and become cosmopolitan.

Its life cycle starts with the female finding the nest of a suitable host where the progeny are in the prepupal stage.

The males hold the female's head in their mandibles, just below the ocelli and maintain antennal contact throughout the ritual which usually lasts 15 minutes.

The newly mature females move to the original oviposition site and release a pheromone which induces nearby females to co-operate in forming a group, called a "chewing circle", which chews through the cuticle of the host allowing the adult wasps to escape.

[1] Female M. australica have been observed excavating access holes through the mud walls of the nests of Pison sp.

Where populations of M. australica are high it can have a noticeable effect on the populations of host species and many of the host species have evolved defences against M. australica including nest location, chemical defences, physical barriers and defensive behaviours.

Where M. autralica is common there can be a high mortality of its host species, which are often pollinators, and so M. australica parasitism can lead to an inhibition in the reproductive and dispersal capabilities of many plants.

[1] In addition, there have been observations of parasitic mites which feed on larvae of the sphecid wasp Sceliphron spp.

[5][4] The bombyliid fly Anthrax angularis and the ichneumonid Stenarella victoriae are parasites in the nests of Sceliphron spp.