l6 THE SENSES OF ANIMALS 



which they live ; they neither smell nor can they taste but 

 they respond to chemical stimuli in a primitive fashion. It is 

 not until we reach the spiders, insects, and similar Classes 

 of creatures that we really come across signs of sensory 

 perception in the way in which we normally use the term ; 

 and even among these groups it is by no means easy to indi- 

 cate which senses predominate; for a certain sense in one 

 kind of insect, for instance, may be lessened or subordinate 

 to another sense in a closely related kind. 



Spiders can certainly see, otherwise they would not per- 

 form such complicated courtship dances as some species are 

 known to carry out. It is obvious that web-building spiders, 

 with greatly varying types of webs, are able to detect the 

 slightest touch or vibration that affects their snares. They 

 can also taste-by-touch as insects do, for they will taste 

 certain food items some of which will be discarded at once 

 — but can they smell? At first thought it is sometimes con- 

 sidered that, as in many higher animals — notably ourselves — 

 the sense of smell and that of taste are very closely linked, 

 there must be an ability to smell if taste is present ; but this 

 is not always so. 



It will be seen, therefore, that web-spiders probably rely 

 mostly on their tactile sense, except during some certain 

 types of courtship ; but hunting spiders can see their prey 

 well so long as it is moving. This question of sight and move- 

 ment will arise again in connection with other kinds of 

 animals. 



In the world of Insects we come across many variations in 

 regard to dominant senses. Dragonflies, for example, have 

 wonderful visual acuity as all can see for themselves if they 

 watch one of the "hawker" species flying up and down its 

 regular beat and at times suddenly going swiftly off course 

 only to return to the original beat a moment later. This 

 deviation from course is for the purpose of catching some 

 insect prey which is frequently as small and fragile a thing 

 as a gnat. Such a performance denotes eyesight of a high 

 degree. On the other hand, there are beetles such as the 

 burying beetles which have a fantastic ability to detect 

 odours at long range ; while the scenting powers of some of 

 the moths seem to be even greater. A male Emperor Moth 



