FORMICOXENUS. 85 



American species belonging to the same or allied genera." However 

 this may be, M . rubida is not found in Britain, whereas F. nitidulus, 

 as shown above, is widely distributed here, but of course it is 

 possible that the former may have inhabited Britain at some 

 far distant period. The nest of F, nitidulus is small and is con- 

 structed from the finer materials of which the hosts' nest is com- 

 posed ; it is generally situated in the interior more rarely in the 

 upper surface of the hillock small galleries connecting it freely 

 with its surroundings. Adlerz 14 found a colony in Sweden situated 

 in the cracks of a rotten oak-stump, over which the host species 

 had built their hillock. 



Wasmann 16 discovered in Holland a small colony, consisting of 

 workers, males, females, and brood, situated in an old cocoon of 

 Cetonia floricola, a beetle which passes its early stages in the nests 

 of F. rufa and pratensis. 



Its colonies are small, not consisting of more than a hundred 

 individuals, and it is not known how a new colony is founded. 

 The male is apterous, mating taking place on the surface of the 

 nest, and I have suggested that after fecundation the females fly 

 away to other rufa nests to lay their eggs, but some probably re- 

 enter their own nest 34 . 



The presence of Formicoxenus in the nests of its hosts may no 

 doubt be explained by the fact that it thus obtains safety from 

 enemies, shelter and warmth in which to rear its brood, and also 

 sustenance, though, as Wheeler 32 remarks, " the nature of its food 

 remains an enigma." It has never been observed to be fed by its 

 hosts, nor to devour the brood of the latter, or their prey I have 

 noticed they will eat honey and also the larvae of Leptothorax 

 acervorum**, and this latter fact is interesting, as Er. Andre described 

 another species of Formicoxenus (F. ravouxi), taken by him in the 

 south of France in a nest of Leptothorax unifasciatus (vide Bull. 

 Soc. Ent. France 1896 367). Colonies of L. acervorum are frequently 

 found in the nests of F. rufa, but it is not suggested that the larvae 

 of the former are the only or proper food of Formicoxenus. 



The relationship between guests and hosts is obscure ; the 

 Formicoxenus moves freely about among the Formica, but is 

 generally treated with indifference ; the latter sometimes threaten- 

 ing with their jaws, but never actually attacking them. When 

 nitidulus meets a rufa it crouches down and remains motionless, 

 and the rufa generally passes on, though sometimes the host may 

 tap its guest with the antennae. 



When the hosts move to another nest, their little guests follow 

 them carrying their fellows and their brood ; an interesting 

 instance of this was observed by Forel 15 in Switzerland. Having 

 several times disturbed a nest of Formica pratensis (which also 

 contained Formicoxenus), the ants deserted it and moved away to 

 an old nest situated at a distance of fourteen metres on August 



