THE SOCIAL INSECTS 



the position of the dish. By including amongst the coloured 

 squares all shades of grey, including the whole scale from 

 dark to light, one can show that the bees are responding to 

 colour and not to mere brightness. A colour-blind animal, 

 such as a dog, cannot distinguish a grey square from another 

 colour of similar brightness. 



By means of such experiments, it can be shown that the eye 

 of the bee is relatively insensitive to the red end of the 

 spectrum but much more sensitive than our eyes to the ultra- 

 violet end. A curious experiment which demonstrates the 

 same point in ants was carried out by Lord Avebury. He 

 found that if the lid of an artificial nest is made of ordinary 

 glass, the ants endeavour to move into shadow, but if 

 Crookes' glass (which cuts out most of the light at the violet 

 end) is used the ants will stay under it. 



Some insects, such as grasshoppers and crickets which 

 produce a lot of sound themselves, have quite elaborate 

 organs of hearing, either in the forelegs or in the abdomen. A 

 female cricket no longer walks towards a singing male if the 

 organs in her forelegs are destroyed, and she can be attracted 

 to a telephone receiver conveying the song of a male from 

 another cage. In other insects, no such organs have as yet 

 been discovered. This is true for instance of the honey bee in 

 spite of the loud hum which it produces. It is possible that 

 some organ is present which has not yet been recognised. 



The sense of smell in a honey bee can be investigated by 

 training experiments, similar to those used to study its vision. 

 A number of dishes can be placed in boxes which may be 

 entered through a small hole. The one dish which contains 

 sugar as well as water can have a scent such as lavender water 

 added to it. Foraging bees can then easily be trained to 

 associate sugar with a particular scent. The honey bee, 

 probably because of the importance of flowers in its economy, 



18 



