There are two species of Forelius in our area. Both are small ants, workers less than 3 mm long and monomorphic. They vary in color from sordid yellowish to blackish, but commonly are reddish with the posterior half or more of the gaster brownish. Colonies may possess many females. Workers forage in dense trails and characteristcally move in a rapid, frenzied fashion. These ants evidently have a high thermal tolerance for the workers may be seen foraging when larger ants have given up.
     One of our species, F. pruinosus, has traditionally been placed in the related genus Iridomyrmex, all New World representatives of which are now placed in the genus Linepithema (Shattuck, 1993). This assignment is one of long standing even though the ant bears little resemblance to others placed there. Indeed, it had been consistently confused with Forelius foetidus (an unavailable name), which it much more closely resembled than any of its supposed congeners. The habitus of F. pruinosus and the structure of the proventriculus are consistent with Forelius and so the ant has been transferred to its present placement. The combination Forelius pruinosus was first formalized by Wheeler and Wheeler (1986), who cited Snelling and George (1979) as the authority for this decision. Most recently, Shattuck (1994) and Bolton (1995) have shown that Buckley's name is unavailable and that the earliest available name is F. mccooki (McCook).
     The species of this largely South American genus have been revised by Cuezzo (2000). Unfortunately, she was evidently unable to examine sufficient material from North America, seriously lessening the validity of her work. She concluded that four species are present in North America: F. analis (André), F. kiefferi (Wheeler), F. mccooki (Forel), and F. pruinosum (Roger). Of these, F. kiefferi is known only from Socorro Island in the Pacific Ocean. Roger described his species from Cuba; according to Cuezzo it is found only in Florida in the United States, but also is found in Mexico. Two species are found in the southwestern and western United States: F. analis and F. mccooki (= F. foetidus).
     In the key, which relies heavily on color, she distinguishes the western species from the other two by the shape of the dorsal margin of the head, concave versus straight. While the figures show a flat margin for both F. kiefferi and F. pruinosus and a concave margin for F. mccooki, in F. analis it is shown to be slightly convex!.
      It is clear, from examination of nest series from any locality, that the shape of the preoccipital margin is variable and not a reliable feature. In most series of both species recognized here, the preoccipital margin is barely perceptibly concave; rarely is it as deeply concave as that illustrated by Cuezzo for F. maccooki and even less rarely as convex as shown for F. analis. In some specimens, it must be admitted, the profile is as straight as those shown for the other two species. It is clear that at least two species are present in the arid regions of the western states; for the present we will adopt the names as set forth by Cuezzo, pending further study of this difficult group.

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