The present study represents an introduction to the revision of Pheidole Westwood, 1839 from Madagascar. Sixteen species groups are established, of which eleven are revised below, and illustrated identification keys to species groups and species of groups revised in this monograph are presented. Two species are raised to species level: Pheidole petax Forel, 1895 stat. nov., and P. scabrata Forel, 1895 stat. nov. We also redescribe worker castes and designate lectotypes for P. annemariae Forel, 1918, P. nemoralis Forel, 1892, P. petax Forel, 1895, P. ensifera Forel, 1897, P. longispinosa Forel, 1891, and P. scabrata Forel, 1895. The following 46 new species are described: Pheidole aelloeasp. nov., P. alasp. nov., P. andapasp. nov., P. ankeranasp. nov., P. avaratrasp. nov., P. bemarahaensissp. nov., P. bemarivoensissp. nov., P. binarasp. nov., P. boriborasp. nov., P. brevipilosasp. nov., P. curvistriatasp. nov., P. diakritossp. nov., P. ehazoarasp. nov., P. ferrugineasp. nov., P. fisakasp. nov., P. fitaratasp. nov., P. glabrasp. nov., P. goavanasp. nov., P. lamperossp. nov., P. longipilosasp. nov., P. luteasp. nov., P. madinikasp. nov., P. mahaboensissp. nov., P. maizinasp. nov., P. makaensissp. nov., P. makirovanasp. nov., P. manantenensissp. nov., P. mantadiasp. nov., P. marieannaesp. nov., P. masoalasp. nov., P. mavesatrasp. nov., P. miramilasp. nov., P. moramanaensissp. nov., P. navoatrensissp. nov., P. ocypodeasp. nov., P. parvioculasp. nov., P. podargeasp. nov., P. praegrandissp. nov., P. ranohirensissp. nov., P. rugocephalasp. nov., P. rugofitaratasp. nov., P. typhlossp. nov., P. vatovavensissp. nov., P. voasarasp. nov., P. vohemarensissp. nov., and P. zavamanirasp. nov. At present, there are 69 valid species and subspecies of Pheidole known from Madagascar, but this number is expected to increase significantly with upcoming taxonomic revisions of the species groups not revised in this study.
