68 Bulletin American Museum of Natural History. [Vol. XXIL 



the shape of mounds as in the European and some of the American 

 ruja forms to be considered presently. The workers collect great 

 quantities of straws, dead leaves, pine needles, etc., and work all this 

 vegetable debris into the crevices of the wood or between the stones. 

 This is clearly seen in PI. IX., Figs, i and 2, and PI. X., Fig. i. 

 When the nests are disturbed the ants bite furiously or congregate in 

 numbers on the surface of the nest, face the intruder, throw their heads 

 back, and, directing the tips of their gasters forward between their hind 

 legs, emit a shower of formic acid. 



Although F. integra seems to be absent in the Mississippi Valley, one 

 of its varieties — hcemorrhoidalis — occurs in the mountains of Colorado 

 at an altitude of 7000-8000 feet. I have observed this form at dif- 

 ferent points in the Ute Pass and the Garden of the Gods, near Manitou. 

 The workers are quite as large as those of the typical integra, but they 

 seem to be covered with a peculiar glaucous bloom. Their habits are 

 very much like those of the eastern form. They do not build mounds, 

 but nest in great logs or stumps or piles of stones in the open woods. 

 The largest nest I have seen was at Woodland Park, where the ants 

 were occupying a prostrate pine log 12 ft. long and i^ ft. in diameter. 

 They had piled up debris to a height of 8-10 inches all around this log. 

 Another nest, apparently belonging to this same colony, was in an old 

 stump. Around this the ants had built a mass of debris 5 ft. in di- 

 ameter at the base and 3 ft. high. This was connected by a run-way 

 with another large nest in a log a few yards away. Like the true i}i- 

 tegra, the var. hcEm,orrhoidalis occurs in the same localities as a form of 

 fusca, in this case not var. sitbsericea but var. argeiitata, a more silver)'- 

 form with reddish legs and antennae. 



The closely allied forms of riifa known as obscunventris, obscnripes, 

 rnbiginosa and melanotica build mound nests, which in Colorado are 

 large dome-shaped accumulations of debris 3 or 4 ft. in diameter at 

 the base and i to 2 ft. high, and hence rivalling the nests of the Euro- 

 pean rufa. In Colorado these nests sometimes occur in colonies in the 

 open pine woods. In the Middle West (Wisconsin and Illinois), how- 

 ever, the nests of obscuripes and melanotica are much smaller and of a 

 different shape, as Father Muckermann has shown. 2 



In 1884 McCook published a number of observations^ on the mound 

 nests of F. obscuripes or an allied form of rufa . These nests were found 



' The Structure of the Nests of some North American Species of Formica. Psyche, Vol. 

 IX, June 1902, pp. 355-360- 



1 The Rufous or Thatching Ant of Dakota and Colorado. Proc. Acad. Nat. Sci. Phila. 

 1884-1885. pp. 57-65. 5 figs. 



