Key to US Formicoxenus species

Key to workers of Formicoxenus species known from the United States, modified from Francoeur et al. (1985).

1

 * Postpetiole large and broadly attached to gaster (articulation only slightly less than height of postpetiole); head with longitudinal rugae along its entire length => 2
 * Postpetiole small and narrowly attached to gaster (articulation approximately one-half height height of postpetiole); head microreticulate, lacking longitudinal rugae => 4

2

 * Dorsum of postpetiole finely but distinctly sculptured, the surface matte; petiole lower, the node rounded dorsally; erect hairs on mesosoma and gaster longer, those on first gastral tergite approximately as long as greatest hind femur diamter. (Associated with Manica invidia) => Formicoxenus chamberlini


 * Dorsum of postpetiole smooth and shiny, at most only very lightly sculptured; petiole higher, the node angular dorsally; erect hairs on mesosoma and gaster shorter, those on first gastral tergite less than 0.8 times greatest hind femur diamter. (Associated with the Myrmica) => 3

3

 * Ventral surface of postpetiole relatively long; propodeal spines relatively long. (Associated with Myrmica incompleta) => Formicoxenus provancheri


 * Ventral surface of postpetiole relatively short; propodeal spines relatively short. (Associated with Myrmica alaskensis) => Formicoxenus quebecensis

4

 * Face above level of eyes areolate overlain with fine, irregular rugae; erect hairs on head and mesosoma swollen and blunt-tipped. (Associated with Formica obscuripes) => Formicoxenus hirticornis


 * Face above level of eyes areolate, rugae absent; erect hairs on mesosoma thin and pointed, those on head a mix of thin and pointed and swollen and blunt-tipped. (Associated with the Formica rufa group) => Formicoxenus diversipilosus