© CSIRO 1998 Australian Journal of Zoology, 1998, 46, 301–315 Revision of the species of the Iridomyrmex conifer group (Hymenoptera : Formicidae), with notes on their biology Steven O. ShattuckA and Peter McMillanB ACSIRO Entomology, GPO Box 1700, Canberra, ACT 2601, Australia. B64 St Ives Northshore, Dampier Ave., Kallaroo, WA 6025, Australia. Abstract The conifer species-group of the ant genus Iridomyrmex is defined and revised at the species level. The species I. conifer Forel, I. setoconus, sp. nov. and I. turbineus, sp. nov. are placed in the group, which is limited to south-western Australia. A key to species is provided and distributions are summarised. These ants show unusual nesting habits in that thatched mounds are used during the cooler winter months and subterranean nests are constructed during the hot summer months. This habit is not known to occur in any other ant. These ants are opportunistic feeders utilising a variety of food sources and will readily relocate nest sites in response to changing resources. Introduction The ant genus Iridomyrmex was recently redefined and its status within the subfamily Dolichoderinae clarified (Shattuck 1992a, 1992b). Unfortunately, the species-level classification within the genus is currently poorly understood and identifications are difficult. In the present study the I. conifer species-group is revised. Three species are recognised in the group, all of which are limited to south-western Australia. The species are morphologically similar, differing primarily in the development of pilosity on the head and mesosomal dorsum. Biologically, these ants are some of the most unusual in Iridomyrmex. One species, I. conifer, has been studied in detail by one of us (PM) and the results of these studies are presented below. It was found that this species uses two distinct nest types: above-ground thatched mounds (Fig. 5) and subterranean nests. Climatic factors influence the type of nest occupied, with mound nests constructed during cooler periods and below-ground nests used during warmer periods. Previous investigations on these ants have been limited. Chemical compounds produced were examined by Cavill et al. (1956) and Blum et al. (1978), and beetles (20 species in 10 families) that occur in I. conifer nests were reported by Clark (1923). Clark (1921) and Crawley (1922) comment on nest structure and Crawley (1922) also mentions these ants preying on lepidopterous larvae. Methods and abbreviations Pilosity characters The abundance and placement of pilosity was found to be of value in diagnosing species within the I. conifer group. However, it should be noted that these hairs are easily abraded and therefore caution should be used when examining older specimens or when limited amounts of material are available. Morphometric characters Size and shape characters were quantified and are reported as lengths or indices. Measurements were made with a stereo microscope using a dual-axis stage micrometer wired to digital readouts. All 10.1071/ZO98033 0004-959X/98/030301.