Pheidole fervens is a medium to large sized species with long limbs. It belongs to the P. fervens clade along with its Australasian congeners P. cariniceps, P. hospes, P. impressiceps, and P. oceanica (Economo et al. 2015). The major workers have strong cephalic rugulae that become reticulated towards the posterior of the head and the minor workers have completely glossy heads with very long antennal scapes. Majors and minors of the species can be separated from those of P. megacephala and P. noda by the postpetiole which is not swollen compared to the petiole (Fig. 3), and the promesonotum which has the large anterior dome in addition to a distinct prominence on the posterior slope (Fig. 5, major; Fig. 43, minor). The minors of P. fervens can also be separated from those of P. megacephala by their larger size and longer antennal scapes (Fig. 39). The majors are easily distinguished from P. megacephala by the very sculptured head (Fig. 13).
Among species treated here, P. fervens is most easily confused with its close relative, P. indica, and the characters used to separate these two are subtle. For both subcastes, the promesonotal prominence is flatter in P. fervens (Fig. 49a, minor; Fig. 63a, major) compared to that of P. indica (Fig. 50a, minor; Fig. 64a, major). The eyes of P. fervens minors (Fig. 65) are relatively smaller than those of P. indica minors (Fig. 66), especially in comparison to antennal segment 10. The propodeal spines of P. fervens are weaker, narrower, and more downcurved in majors of P. fervens (Fig. 63b) compared to those of P. indica (Fig. 64b). Readers are referred to Eguchi (2004b; 2008) for characters used to separate P. fervens and P. indica from their Asian congeners.
In the Pacific Island region P. fervens is often confused with the nearly identical P. oceanica, which is native to that region. The carinae between eye and mandible are branching and reticulated in the majors of P. fervens (Fig. 67), versus parallel and not reticulated in those of P. oceanica (Fig. 68). This character was erroneously reversed in the key provided in Sarnat and Economo (2012). The minors are more difficult to separate, but in P. fervens the length of propodeal spine is equal to or less than the diameter of propodeal spiracle (Fig. 69), whereas in P. oceanica it is greater (Fig. 70).