ii FOOD OF INSECTS 43 



accede to some request. The caress has the desired 

 effect, for the aphide responds to the call by eject- 

 ing a drop of liquid which the ant greedily laps up ; 

 the aphide in fact acts as the ant's cow. No use of 

 the secretion to the aphides themselves has been 

 recognised; probably, since it is sticky, it is to their 

 advantage to have it removed. This liquor forms the 

 principal nourishment of many ants, of the red and 

 - yellow kinds in particular, the different species of 

 ants being chiefly devoted to different species of 

 aphis. 



Towards the aphides of their choice ants extend 

 special guardianship and protection, treating them as 

 their own private property, and resenting on part of 

 them all interference offered by other insects. Some 

 take possession of a branch where their cattle 

 browse, and hold it against intruders by vigorously 

 attacking any aggressor. They serve as an efficient 

 standing army to the aphides in return for the 

 food that the latter furnish. Some ants build little 

 walls of earth over their aphides, cow-sheds they 

 may be called, to prevent them straying. Some 

 form a private covered roadway between their cattle's 

 grazing ground and their nest, placing their cows 

 within easy reach and distance of communication. 

 Others of these ingenious beings, who are always 

 busy, have taken to heart the lesson of the necessity 

 of the economy of time and labour. To save them- 

 selves repeated and tiresome journeyings to and fro, 

 they frequently thoroughly domesticate their cows, 

 so to speak, or drive them in considerable flocks 

 into the near neighbourhood of home ; sometimes 



