34 THE SENSES OF ANIMALS 



and also at times some distance from water ; they will often 

 come into gardens to hunt their insect prey. Some of these 

 long-bodied Hawkers will be found on the wing from mid- 

 June to September, or even in October in one or two species. 



They often have "beats" up and down which they will 

 fly regularly — particularly in woodland rides and in gardens. 

 This habit makes them easier to watch. Their prey will 

 vary from occasional butterflies and true flies to mos- 

 quitos and gnats. 



I have spent many hours watching them when feeding, 

 and I have found that it is best to begin by relying on the 

 naked eye so that a general idea of their beat and the time 

 they take to cover it may be obtained. They fly fast, and 

 every now and then they will deviate suddenly and at in- 

 creased speed from their normal course. This is when they 

 have seen a possible victim to catch in their first pair of legs. 

 Should the insect that has attracted their attention be a 

 butterfly, there will be no difficulty in seeing the dragonfly 

 seize its prey and there will be no need to use the binoculars ; 

 but as, more often than not, it is a tiny flimsy insect that is 

 scarcely visible to our human eyes, the binoculars will enable 

 one to see the capture if it is not made at too long a range. 



The mere fact that the dragonfly can sight and then seize 

 insects varying in size from butterflies to gnats, shows the 

 focal adjustments that can be made instantaneously ; and it 

 will also demonstrate the keenness of vision that enables the 

 hunter to see a gnat at all when flying at considerable speed. 

 Dragonflies are quite long-sighted and can see prey at ten 

 or fifteen yards' distance. 



I must point out that the dragonflies do not always catch 

 the intended victim : they do at times miss their mark ; but 

 I have gained much satisfaction from my observations, and 

 have increased my knowledge of the eyesight of dragonflies 

 at the same time. 



Spiders 



Seeking practical evidence in the field of the way that spiders 

 use their eyes is not at all simple, and I think that field 

 observations on spiders are more productive of results when 



