THE SOCIAL INSECTS 



than another. Thus the shining jet black ant, Lasius fuli- 

 ginosus, mainly follows a scent-trail, like a blood-hound. 

 In this species well-beaten trails are formed, often visible to 

 the naked eye since most movable rubbish has been cleared 

 away. Down these trails rather dense, close columns of the 

 foragers may often be seen marching. On the other hand, 

 the common British black ant, Lasius niger, mostly uses its 

 eyes to see the way and has much more indefinite trails, 

 along which it usually goes singly. Most species, however, 

 can when necessary use senses other than the favourite one. 

 The black ant, for instance, certainly makes use of scent as 

 well as of sight. 



One method by which ants can find their way is known as 

 the " sun compass reaction ", and was first studied in North 

 Africa by Santschi about forty years ago. When using the 

 sun as a clue to the direction, ants will continue to walk on a 

 path parallel to the one leading to the nest even if they are 

 picked up and put down some way off the track. They also 

 distinguish between the way to and the way from the nest. 

 This is probably accomplished by arranging that the sunlight 

 falls on one eye so that the ants walk at a constant angle to it. 

 In the short time necessary for making one journey the sun 

 does not move enough to make the method inaccurate. But 

 when an ant is confined for two or three hours in a dark box, 

 placed over the track, the sun will move through an appreci- 

 able angle. As a result, when the ant is liberated it takes a 

 course which makes about the same angle to what would 

 have been the correct course at the time it was first confined. 



Carthy, in London, has recently studied the way-finding 

 of the jet black ant and the black ant in a small artificial arena. 

 The glass floor of the arena can be turned round independ- 

 ently of the circular sides. Some grubs are placed in the 

 centre and a worker is allowed to enter through a hole in the 



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