Species 4 generally refers to the southern free-tailed bat, although it has been separated into eastern and western populations at times.

Morphological attributes that aid in identification are forearm length, mass and colouring[6] however there are a number of similar species in the genus, such as M. petersi.

This species possess the largest glans penis of the genus Mormopterus, on average greater than 9 mm and of a distinctive shape.

[1] The species is found across a number of vegetation types including mallee, shrubland, open forest and woodland, with a preference for wetter environments.

It uses echolocation to locate its insect prey and feeds in or above the open canopy, also taking advantage of gaps in trees (including edges and roads).

In Victoria they have been found to feed on the Rutherglen bug (Nysius vinitor) which is considered an agricultural pest.

Females were found to be able to store sperm for up to two months to conceive during optimal times; a characteristic unknown in other species of mollossidae.

The IUCN currently classifies the southern free-tailed bat as Least concern due to its wide distribution and common occurrence, although population numbers appear to be declining in certain locations.