THE SENSES OF INSECTS 113 



That the sense of smell is very acute among insects 

 cannot be doubted. Indeed, those who have studied 

 insects most closely agree that their behaviour is largely 

 governed by impressions transmitted to the nerve-centres 

 from olfactory end-organs. The latter are often present 

 upon the palpi, but they are generally most numerous 

 upon the antennae, which may be regarded as a pair of 

 highly efficient noses — though not, of course, to the ex- 

 clusion of other functions for which they may be fitted. 

 If we dip a glass rod into strong-smelling liquid, such as 

 acetic acid or turpentine, and bring it near to an insect, 

 we shall notice that the antennas are immediately moved 

 vigorously about ; while they may subsequently be cleaned 

 by being drawn through the mouth, as though to purge 

 away the last vestiges of the pungent vapour. Many 

 insects, such as flesh-flies, carrion-beetles, and flower- 

 frequenting species of all kinds, detect the whereabouts 

 of their favourite food by means of their antennas; and 

 those individuals in which these organs have been 

 destroyed or mutilated are liable to perish by starvation 

 in the midst of plenty, for they become quite indifferent 

 to the odours which guide their uninjured companions. 

 In some insects the olfactory sense is well-nigh incredibly 

 keen. Thus, all the ants of a given colony are believed, 

 not without reason, to possess a characteristic nest-smell, 

 by means of which they recognise one another and detect 

 the presence of strangers ; while other communal insects, 

 such as bees and wasps, appear to be similarly gifted, for 

 they are quick to welcome friends, even after months of 

 separation, and never fail to drive away intruders. Even 

 more wonderful is the manner in which other insects, 

 especially certain moths, track down their mates by means 

 of their sense of smell. The antennas of the male are 

 often marvellous structures, plumed or branched, and 



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