THE COMPOUND NESTS. 43 l 



indifference. Some observers have occasionally noticed slight indica- 

 tions of hostility between the two species. When the rufa moves to 

 a new nest the Formicoxeni follow in the files of the host, carrying 

 one another and their brood. None of the authors above mentioned, 

 notwithstanding the closest observations, has been able to detect any 

 other relations between the inquiline and its host. The rufa are never 

 seen to feed the inquilines, and the latter have never been seen to eat 

 the progeny of their host or the dead insects brought into the nest, so 

 that the nature of their food remains an enigma. 



Formicoxenus nitiditlns is, moreover, an interesting species, because 

 the male, 'discovered by Adlerz in 1884, is wingless and highly ergato- 

 morphic. It can be distinguished from the worker only by the more 

 curved antennal funiculi and their additional joint, the presence of 

 stemmata (which, however, occur also in some workers), the addi- 

 tional gastric segment and the genital appendages ; the eyes, head, 

 thorax and legs are remarkably like those of the worker. The wingless 

 condition of this male makes a nuptial flight impossible, of course, so 

 that mating has to take place on the surface of the Formica nest or 

 on the ground and stones in the neighborhood. The mating has been 

 seen by several European observers, and during July, 1907, I had an 

 opportunity to witness it near Samaden, on the slopes of Piz Ot, at an 

 altitude of about 2,000 m. in the Upper Engadin. After a cold night, 

 the sun remained behind a mass of clouds at about 9 A. M. when I saw 

 dozens of Formicoxeni of all three phases, but mostly males, running 

 hither and thither over the small twigs and other debris forming the 

 outer covering of an old rufa nest which I had stopped to examine. 

 The males moved very quickly, with feverishly vibrating antennse, and 

 were so amorous that they often seized workers and attempted to mate 

 with them. The few winged females were soon supplied with partners 

 and the supernumerary males continued to hurry about over and among 

 the little sticks of the nest. Then the sun suddenly emerged from the 

 clouds and, as if by magic, all the Formicoxeni disappeared into the 

 nest. I waited for some time and during the remainder of the morn- 

 ing returned repeatedly to the spot, but none of the tiny inquilines 

 reappeared. 



2. Formicoxenus ravouxi and corsicus. These two species are 

 known only from female specimens. The former was taken in France 

 by Ern. Andre (18930) in a nest of Leptothorax unifasciatus. The 

 host of the latter species is unknown. 



3. Xenomyrmcx stolli. Forel ( 1884^) described this small, shining, 

 dark-brown ant, which is allied to Monomorium, from some specimens 

 found in Guatemala, living in a huge oak-gall in company with a much 



