Phediole is a taxonomically challenging genus. These main issues arise from, but are not exclusively due to, the incredible species diversity within the genus and the wide range of variability exhibited by their dimorphic workers. One way taxonomists have tried to help manage Pheidole diversity is to organize morphologically similar species in a region, or in two adjacent regions, into species groups.
Pheidole diversity is at its highest in the Neotropics. A much needed revision of the many hundreds of species occurring there was accomplished as part of an audacious taxonomic study of all the New World Pheidole (Wilson 2003). Wilson's study organized the 625 species it treated into 19 species groups (as detailed here: New World Pheidole). The large number of species and extensive geographic extent in this revision made the species groups used arguably less helpful for identification than groups created in other regions. It can be a daunting task to work a specimen through the keys presented in Wilson's revision. For those less familiar with Phediole, either generally or in terms of a local fauna, being slightly uncertain anywhere in the species group key or the subsequent key to species within a group can be extremely problematic. Also, for identification it is very helpful to have a worker series that includes both minor and major castes. This is often not the kind of collection one has on hand. Jack Longino presented the use of data matrixes, with an array of discrete and measured characters, for identification. Using this approach, as little as five quantifiable characters recorded from a specimen can reduce the number of possible species it is to a small number of possibilities. Once the species pool is limited enough, one can make a determination based on comparisons with images and descriptions available online for each possible species.
The geographical coverage of specimens used in Wilson's 2003 revision was good for North America, through Central America, and into the Amazon Basin. Our understanding of the Pheidole species occurring here now stands on a solid foundation. New species can more easily and readily be identified as such, and future research can add to and refine what is known about Phediole in these areas. The New World Pheidole south of the Amazon basin had much poorer coverage. It can be hard to impossible to determine Pheidole specimens found here to species. Alexandre Cascade-Ferreira has recently began working on this problem and aspires to revising all the Pheidole found in the southern half of South America.
Pheidole in other regions of the world have been treated in various taxonomic studies. The following pages provide information about Pheidole species groups in places beyond the New World.