64 ANIMAL INTELLIGENCE. 



workers returning to the nest from the tree on which the milk- 

 ing was going on, a far smaller number had distended abdomens 

 than among those descending the tree itself. A closer investi- 

 gation showed that at the roots of the trees, at the outlets of 

 the subterranean galleries, a number of ants were assembled, 

 which were fed by the returning ants after the fashion already 

 described in feeding the larvae, and which were distinguished 

 by the observer as ' pensioners.' MacCook often observed the 

 same fact later, among, with others, the alrrady described 

 Pennsylvanian wood-ant. Distinguished individuals in the 

 body-guard of the queen were fed in like fashion. MacCook is 

 inclined to think that the reason of this proceeding is to be 

 found in the ' division of labour ' so general in the ant repub- 

 lic, and that the members of the community which are em- 

 ployed in building and working within the nest, leave to the 

 others the cai*e of providing food for themselves as well as for 

 the younger and helpless members ; they thus have a claim to 

 receive from time to time a reciprocal toll of gratitude, and 

 take it, as is shown very clearly, in a way demanded by the 

 welfare of the community. 1 



Aphides are not the only insects which ants employ as 

 cows, several other insects which yield sweet secretions 

 being similarly utilised in various parts of the world. 

 Thus, gall insects and cocci are kept in just the same way 

 as aphides ; but MacCook observed that where aphides 

 and cocci are kept by the same ants, they are kept in 

 separate chambers, or stalls. The same observer saw 

 caterpillars of the genus Lycoena kept by ants for the sake 

 of a sweet secretion which they supply. 



Habit of making Slaves. This habit, or instinct, 

 obtains among at least three species of ant, viz., Formica 

 rufescens, F. sanguinea, and strongylognathus. It was 

 originally observed by P. Huber in the first-named species. 

 Here the species enslaved is F.fusca, which is appropriately 

 coloured black. The slave-making ants attack a nest of 

 F. fusca in a body ; there is a great fight with much 

 slaughter, and, if victorious, the slave-makers carry off the 

 pupae of the vanquished nest in order to hatch them out 

 as slaves. Mr. Darwin gives an account of a battle which 

 he himself observed. 2 



1 Loc. cit. p. 123. 



2 Origin ofSpeoics, 6th ed. p. 218. 



