The following account is from Sarnat et al. (2015).
Pheidole proxima is a relatively small, brownish yellow, short-limbed species with a strongly shining integument. They phylogenetic placement of P. proxima is unknown, but it almost certainly clusters within an Old World clade that has radiated across Australia and New Guinea. The species is slightly smaller than P. megacephala, but both have workers with almost entirely glossy faces. The postpetiole of P. proxima is not swollen relative to the petiole (Fig. 3), as it is in P. megacephala. The head of the major is subquadrate, while that of P. megacephala is more heart-shaped. The antennal scapes of the minor do not surpass the posterior head margin, as they do in P. megacephala. The other two Pheidole species established in New Zealand are P. rugosula and P. vigilans. The glossy face of P. proxima easily separates both worker castes of from those of P. rugosula. In addition to being significantly smaller (major HW < 1.0 mm, minor HW < 0.48 mm) than P. vigilans (major HW > 1.2 mm, minor HW > 0.52 mm), the major of P. proxima is more sculptured, and the hypostomal bridge has a distinct median tooth. The minors of P. proxima are separated from those of P. vigilans by the shorter scapes, more sculptured mesopleuron, and more robust propodeal spines. Additional taxonomy of these species is discussed in (Berry et al. 1997).
Comparison of the Pheidole proxima Mayr type series and images of the two subspecies suggests that all three taxa are heterospecific. There is some reason to believe, however, that the name P. proxima Mayr does not apply perfectly to the species recently introduced to New Zealand. The specimens examined from New Zealand conflict with Mayr’s original description and type specimens on several points. The pronotal dorsum of the type major worker is transversely rugose whereas that of the New Zealand specimens are completely glossy. Although we were unable to examine minors from the type series, Mayr described the head of the minor worker as coriaceous and striate-rugose with scapes that barely exceed the posterior margin. In contrast the minor workers from New Zealand have heads that are completely glossy and scapes that do not exceed the posterior head margin. Forel, in his description of P. proxima subsp. bombalenis, describes the minor worker as identical to P. proxima Mayr with the exception of having longer propodeal spines. The specimen images of the P. bombalensis syntype minor show a strongly sculptured face, similar to the pattern described by Mayr. The major workers from the type series are larger than the New Zealand specimen we measured (HW 1.03–1.05 mm vs. HW 0.95 mm), have relatively narrower heads (CI 87–89 vs. CI 92), and relatively shorter antennal scapes (SI 42–46 vs. SI 52). While a more exhaustive survey of Australia’s Pheidole may reveal the New Zealand population to be more closely related to another species from that fauna, we follow Berry et al. (1997)in using P. proxima Mayr.