wheeler: ants of the genus formica. 433 



form only in Illinois. These are much smaller than the nests of the 

 typical aggeraus, being rarely more than a foot or 18 inches in diame- 

 ter. They are built of coarse materials in open grassy fields. Appar- 

 ently melanotica in its deeper pigmentation and its fondness for such 

 situations and for lower altitudes bears about the same relation to 

 aggeraus that F. pratcnsis does to the typical rufa in Europe. 



29. F. RUFA OBSCURiPES Forel. 



F. rufa St. obscuripes Forel, Ann. Soc ent. Belg., 1886, 30, C. R. p. xxix; 



Ibid., 1904, 48, p. 152, ^ ; Wheeler, Ants, 1910, p. 570. 

 F. rufa obscuriventris Mayr var. obscuripes Emery, Zool. jahrb. Syst., 1893, 7, 



p. 644, 650, S . 



Worker. Length 3.8-8 mm. 



Similar to the typical rufa of Europe, but the large individuals 

 have the head and thorax of a lighter red and entirely or almost en- 

 tirel}^ without dark spots on the head and thorax, whereas the legs 

 and petiole are blackish brown or reddish brown. The small workers 

 are of a much darker color and have the head and thorax spotted with 

 brown. Gaster subopaque, deep brown or blackish, covered with 

 slightly longer and denser, gray pubescence than the typical rufa, 

 while the erect hairs on the gaster, head, and thorax are rather sparse, 

 inconspicuous and less numerous than in the true rufa and the sub- 

 species pratensis. Tibiae without erect or suberect hairs and covered 

 merely with appressed pubescence. Gula with a few erect hairs. 

 Eyes hairy. 



Host (Temporary). Unknown; probably one of the boreal forms 

 of F. fusca. 



Type locality. — Wyoming : Green River (S. H. Scudder) . 



Wyoming: Elk Creek (R. P. Currie). 



Montana: (Amer. Mus. Nat. Hist. Coll.). 



Washington: Loon Lake (S. Henshaw) ; Rock Lake (A. L. Melander). 



Colorado: Boulder (Wheeler). 



Arizona: Thatcher (R. V. Chamberlin). 



British Columbia: Golden (W. Wenman); Summerland (W. H. 

 Britton). 



This form is imperfectly known. Forel insists on regarding it as a 

 subspecies, and he may be right, but it should be pointed out that the 

 absence of erect hairs on the tibiae is perhaps not as strong a character 

 as he supposes. One often finds workers of what I regard as Emery's 

 ruhiginosa (aggerans) that have very few suberect hairs on the tibiae. 



