THE ANTS OR PISMIRES 



sides, find the grubs, and start carrying them back to the nest. 

 While the ant is at the centre, it can be confined in a small 

 thimble and the arena rotated. Some species, such as the 

 black ant, are not much disturbed by this rotation, but 

 usually set off in the right direction. They probably mainly 

 use their eyes to find the way. The jet black ant, on the 

 other hand, is usually nonplussed. It tends to follow the old 

 scent-trail, and this, after the rotation, no longer leads to the 

 door in the wall. Carthy was able to make the scent tracks 

 visible by dusting them with very fine Lycopodium powder. 

 The track appears to be formed by liquid excreta which is 

 ejected when the abdomen is dragged over the floor. In 

 another ant, Myrmica, Macgregor showed that the track 

 consisted of a discontinuous series of pear-shaped spots. 



Some of these ants are also sensitive to the plane of polari- 

 sation of light, like the honey bee. The light by which the 

 ant finds its way across the arena can be polarised by passing 

 it through a sheet of " polaroid ". If then, before the return 

 journey, the sheet of polaroid is rotated through an angle, 

 the ant is much less certain of the correct way back. There 

 seems little doubt that with further experiments much more 

 will be discovered about how ants find their way to and from 

 the nest. In so far as all the ants in one nest use the same 

 tracks, this already has some social significance, but any 

 discovery of definite system of intercommunication would 

 have much more. 



The special feature of the social life of ants, compared 

 with that of bees or wasps, is the much wider range in 

 behaviour and in type of social organisation. This is partly 

 because there are many more kinds of ants than there are of 

 the other social Hymenoptera. This in turn is to some 

 extent a reflexion of the long period over which they have 



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