43 ANTS. 



further investigation. It is quite probable that C. tcnnitarius may be 

 carnivorous and represent merely an additional case of lestobiosis. 



F. Xenobiosis. 1 have given this name to certain types of com- 

 pound nests in which the relations between ants of two different species 

 are of a very definite and intimate character. In these cases one of the 

 species, known as the inquiline, or "guest ant," can live only in asso- 

 ciation with a host, and unlike several of the species included under the 

 preceding captions, is never found living alone. Although the guest 

 ants live with their hosts on terms of mutual toleration or even friend- 

 ship, each species rears its brood in chambers of its own excavation. 

 In midsummer, however, when these broods mature, individuals of all 

 three phases of both species are found intermingled, moving about in 

 the chambers of the host and freely consorting with one another. This 

 condition is rarely seen in any other forms of social symbiosis, for in 

 the mixed colonies, to be considered in the following chapters, the 

 sexual phases of the host species are, in nearly all cases, suppressed. 



i. Formicoxenus nitidnlns (Fig. 259). The habits of this small, 



FIG. 259. Formicoxenus nitidnlns. (Original.) a, Worker; b. ergatomorphic male. 



slender, shining, yellowish-red ant, which much resembles certain spe- 

 cies of Leptothorax, have been described by Adlerz (1884), Forel ( 1874, 

 i886d), Wasmann ( 1891/1) and Janet ( 1897?). I* ' s a sub-boreal species 

 and nests only in the interior of the great debris mounds of Formica 

 rnfa and F. pratensis. Here it excavates small chambers which commu- 

 nicate by means of slender passages with the galleries and chambers of 

 its much larger hosts. Wasmann found a colony of Formicoxenus 

 inhabiting the cavity of an old cocoon of Cetonia floricola, a chafer 

 which passes its larval and pupal stages at the bottom of rnfa nests. 

 The guest-ant moves about freely among its host who treats it with 



