THE SENSES OF INSECTS 111 



upon one kind of flower to the exclusion of all others; 

 that ants and bees can detect certain inodorous substances 

 which have been mixed with honey. These are well- 

 established facts ; but they do not prove that insects can 

 taste. Half-grown caterpillars will often starve rather 

 than renounce their ancestral diet ; yet the same kinds of 

 caterpillars, when just hatched, will readily adapt them- 

 selves to a quite different food. This is not always the 

 case, but it is sufficiently common to suggest that their 

 fastidiousness in later life is largely a matter of habit, 

 possibly based upon the sense of smell, but having little 

 or nothing to do with that of taste. Again, the prefer- 

 ence which certain insects display for a particular kind of 

 flower is not necessarily the outcome of deliberate choice. 

 In many instances it is governed by the insect's mouth- 

 parts, which may be too long or too short, or in some way 

 unfit to probe successfully more than a limited number of 

 the blossoms which it may encounter. For the insect and 

 flower have been evolved through long ages of mutual de- 

 pendence, and have become inseparable. The one matches 

 the other as a key fits a lock ; and if the former is quick 

 to perceive where its welcome is sure, and to pass over 

 blooms whose sweetness is reserved for other visitors, its 

 guiding senses are probably those of sight and smell. 



The French savant Forel mixed morphine and strych- 

 nine with honey and offered it to bees. They refused 

 the concoction after a first mouthful. Similarly, Will 

 accustomed wasps to visit a particular spot for powdered 

 sugar, and then replaced the sugar by alum. The wasps 

 ate some of the latter, soon detected the change, and 

 began rubbing their mouth-parts to cleanse them. To 

 quinine also they evinced an obvious dislike. But the 

 evidence of these and other experiments tends to show 

 that the insect gains its impressions of what it is eating 



