SIGHT — FIELDWORK AND EXPERIMENTS 33 



Stamping, otherwise the combination of the light and earth 

 vibrations would lose me the worm. 



More likely to be spotted are those worms with their tails 

 still in their holes, and catching them is no easy task. It is 

 no use flashing your light to guide you and trying to pick up 

 the worm by its body at the same time. I have always found 

 that the worm could withdraw into its burrow before I could 

 get it. Put your torch gently on the ground and put your 

 thumb firmly on the place where the worm's tail enters the 

 hole. Then if you are lucky you can grasp the worm with 

 your other hand before it can get too strong a hold with its 

 tail. The light, without which you can't do much, will 

 stimulate the worm to make a retreat from it; so quick 

 movement and quiet approach is the only way of defeating 

 the earthworm's fantastically swift reaction to strong light. 

 This may seem to be an involved and lengthy description 

 of how to catch worms, but nothing that I know of will 

 demonstrate so well how sensitive worms are to light, even 

 though they do not possess "sight" in its true sense. 



Insects 



There are so many species of insects that it is not easy to 

 select one or two which will in the field demonstrate their 

 ocular efficiency and, at the same time, be possible to observe. 

 Binoculars are so associated with bird watching that it may 

 seem almost absurd to think of using them to watch the 

 behaviour of insects ; but as I consider that dragonflies, for 

 example, bring home to one their amazing powers of sight 

 better than any other insect, I can strongly recommend the 

 use of field-glasses as an aid to observation. 



The larger dragonflies are, of course, the best kinds to 

 watch, not only because their size makes following their 

 flight easier but because they will take larger prey than their 

 smaller relatives. Of these large species, the ones known as 

 the long-bodied Hawker Dragonflies, are the most satis- 

 factory. (See Plate i.) 



They measure about three and a half inches across the 

 wings and two and three-quarter inches in body length. 

 They are to be found flying near and over ponds, canals, 



