Genus Tapinoma Foerster

T. melanocephalum (Fabricius) is an introduced species, not definitively established in the state. T. sessile (Say) is a very common ant, found in almost all habitats in California except deserts and areas invaded by Linepithema humile. T. sessile shows substantial variation in size and color. At scattered locations in California a bicolored (orange and black) form of T. sessile occurs sympatrically with the typical unicolored dark brown/black morph. Workers of intermediate color have also been observed, suggesting that the two forms are conspecific. An alternative interpretation is that there are two species which occasionally exchange genes, perhaps analogous to the situation between Forelius mccooki and F. pruinosus and between Dorymyrmex bicolor and D. insanus.

Species identification: key in Creighton (1950a). Additional references: Meissner and Silverman (2001), Smith (1965), Wang and Brook (1970).