194 MINUTE MARVELS OF NATURE 



process the creature has the juices of his victim at 

 his disposal. 



The spider has many weapons with which to 

 hold its own, but on the other hand it has many 

 weapons opposed to it. There are some kinds of 

 wasps which feed their young' upon nothing but 

 spiders ; and you have only to watch a spider that 

 has a bee in its web to see that it understands 

 what a sting means. It may be said, however, 

 that the spider chiefly lives on flies, which have 

 practically no weapons to defend themselves. 

 Yet it is worth while to see a fly's foot under a 

 good microscope (Fig. 128) (and a fly has six feet). 

 Tne fringed pads are the means (assisted by the 

 sharp claws) by which it performs that familiar 

 but curious feat ot defying the laws of gravity 

 and walking upon the ceiling. The claws get a 

 certain hold in the tiny crevices, too small for our 

 eyes to see, while the pads are furnished with a 

 large number of trumpet-shaped hairs, which 

 secrete a viscid fluid of sufficient strength to bear 

 the insect's weight. And so in autumn when flies 

 begin to die, we frequently find them quite dead, 

 yet holding firmly to our walls and windows. 

 This happens when the viscid fluid has been duly 

 secreted, but the fly has become so weakened 

 that it has been unable to detach its feet again. 



While considering these curious pads of the foot 



