356 



PSYCHE. 



[June, iqo2 



namely Fo?-jnka ohsctiripes For. It is 

 one of the most ferocious ants to be 

 found here and to it alone may be ap- 

 plied his remarks concerning Formica 

 Integra Nyl. in the east, namely that like 

 the European F. praiensis, it " rises upon 

 its hind legs, curves the abdomen and 

 ejects .... some venom while in this 

 position " (/. c. 233). According to my 

 experience the ejection of formic acid 

 is so copious, as to force the observer to 

 retire momentarily, especially during the 

 main breeding season. Of these ants I 

 know at least 35 nests in this neighbor- 

 hood. All without exception consist of 

 elevated conical mounds, whose shape is 

 more or less modified according to its 

 age and the number of inmates. I had 

 occasion to observe the nests as well in 

 their inception as in the different stages 

 of their development. In founding a 

 new colony this species, unlike many of 

 its relatives, does not choose a shady 

 spot ; on the contrary, the favorite situa- 

 tion of F. obscuripes is in the middle of 

 an open meadow, on some exposed rail- 

 road embankment, in fine, wherever the 

 sun pours down its full measure of heat. 

 The little squadron sallying forth to 

 establish a new foundation no sooner 

 discover a warm, sunny place, than they 

 begin to dig a few holes in the soil, 

 whence there arises gradually a little hill. 

 At the same time straws, small twigs, 

 dry blades of grass, and the like are zeal- 

 ously gathered by the indefatigable 

 workers and, mixed with earth, are 

 heaped on the hill. If the number of 

 workers is considerable there arises 



within a short time a domelike structure 

 of variable dimensions up to 75 cm. in 

 diameter and 40 cm. in height, bearing a 

 resemblance to some of the famous 

 Indian mounds abounding in this region. 

 Still the nest has not yet its characteris- 

 tic form, which seems to prove the most 

 advantageous both for the adult individ- 

 uals and especially for the undeveloped 

 brood. The entrances are concentrated 

 more and more in the central part of the 

 dome surface. This surface is at first 

 somewhat flattened, later on even hol- 

 lowed out, so that under favorable cir. 

 cumstances the out^r slopes of the hill 

 appear entirely abandoned, so much so 

 as to allow grass to cover them. There- 

 by, however, the nest is enclosed, as it 

 were, by a massive rampart which proves 

 an excellent protection against the ex- 

 treme changes of temperature. By the 

 same means, moreover, the ants succeed 

 in hiding their nests to some degree, 

 especially in spring time, when the new 

 generation is being developed. Thus it 

 may happen, that at this season the 

 nests which are otherwise so conspicuous, 

 may elude even a careful search. Of 

 course in summer, after the grass is 

 burned up by the sun, they are all the 

 more noticeable. But at that time the 

 ants are compelled by the excess of heat 

 and want of humidity to retire to the 

 lower compartments and ordinarily ap- 

 pear again only after a rain and on 

 moderately warm days. Generally speak- 

 ing, the main working season of our 

 ants is in the early springtime. During 

 summer and autumn they are found only 



