The following account is from Sarnat et al. (2015).
Pheidole rugosula is a small, brownish yellow, short-limbed species with moderate head sculpturing that most likely belongs to the Australian-New Guinea clade that includes close relatives of P. variabilis Mayr. The head sculpturing of both the major and the minor is distinct among all other Pheidole species treated here. These characters easily separate P. rugosula from P. megacephala. These same characters, together with a more sculptured promesonotal dorsum (Fig. 20, major) and stout propodeal spines, can be used to separate P. rugosula from its two other congeners that are established in New Zealand, P. proxima and P. vigilans (which is also much larger, major HW > 1.20 mm). There is a bewildering diversity of native Australian (and to a lesser extent New Guinea) Pheidole that approach the morphology of P. rugosula. Additional characters for identifying New Zealand Pheidole species are provided in Berry et al. (1997). A significant revision of the P. variabilis group is required before P. rugosula can be reliably separated from these species.
In New Zealand, P. rugosula is strongly associated with human disturbance and is the most commonly encountered of the four Pheidole species established in New Zealand (Berry et al. 1997). It has been recorded frequently from gardens, orchards, structures and urban areas. The species was reported nesting in compost, in the soil of vegetable gardens, in the soil of lawns, and near rubbish baskets (Berry et al. 1997; Harris et al. 2005b). It has also been recorded as scavenging dead arthropods, human food waste, nuts and seeds, and is often found associated with rotting fruit (Berry et al. 1997; Harris et al. 2005b). Other collection records suggest P. rugosula will forage arboreally. Berry et al. (1997)also mention that label data suggests the species was collected several times attacking ootheca of mantids, including those of the native mantid Orthodera novaezealandiae (Colenso).
Pheidole rugosula is considered to be a nuisance pest around urban areas in New Zealand (Harris et al. 2005b), where foragers are attracted to pet food left out and to windfall fruit. Although it occurs in native habitats in New Zealand, its impacts are unknown. Collection data indicating a P. rugosula attack of native mantids suggest it could have some negative impact on native biodiversity, however.
Diagnosis among introduced Pheidole. Body reddish brown to nearly black. Major | HW 0.86–1.06, HL 0.94–1.13, SL 0.56–0.63, CI 92–97, SI 57–68 (n=9, Longino pers. comm.). Head bicolored with the yellowish posterior two-thirds contrasting with the darker brown anterior third and rest of body. Head subquadrate; often entirely foveolate, but portions of posterolateral lobes can be glossy. Posterolateral lobes never with distinct rugae. Promesonotum in profile forming a single dome, lacking a distinct mound or prominence on the posterior slope. Promesonotal dorsum usually foveolate and never with distinct transverse striae. Postpetiole not swollen relative to petiole. Postpetiole relatively broad; distinctly more than 2x petiolar width in dorsal view. Gaster with at least anterior 1/3 of first tergite matte. Minor | HW 0.44–0.50, HL 0.54–0.59. SL 0.55–0.58, CI 79–85, SI 114–125 (n=14, Longino pers. comm.). Head, including the area mesad of the frontal carinae, entirely covered by reticulated network of punctures. Posterior head margin relatively narrow. Antennal scapes lack standing hairs; scapes surpass posterior head margin by a distance equal to or greater than eye; scapes relatively long (SI 103–125). Promesonotum in profile forming a single dome, lacking a distinct mound or prominence on the posterior slope. Hairs on mesosoma stout, stiff, of equal length and arranged in pairs. Postpetiole not swollen relative to petiole. Postpetiole broad in dorsal view, distinctly broader than petiole. Gaster with at least anterior 1/3 of first tergite matte.
Pheidole rugosula is believed to be native to the New South Wales region of Australia. The only country where the species has established is New Zealand (Berry et al. 1997). Berry et al. (1997)published museum records of P. rugosula from New Zealand. The first known occurrence of P. rugosula in New Zealand is from Takapuna, where it was collected in 1958 and it had reached Auckland by 1963. Since then it has been found across the Auckland and Waikato regions.