FOOD OP INSECTS. 419 



liewed either wholly, or at least their concentric circles, 

 every twenty-four hours, even when not apparently 

 injured. This difference in the operations of the two 

 tribes depends upon a very remarkable peculiarity in 

 the conformation of their snares. The threads of the 

 house spider's web are all of the same kind of silk, and 

 flies are caught in them from their claws becoming- en- 

 tangled in the fine meshes which form the texture* 

 On the other hand tlie net of the garden spider is com-* 

 posed of two distinct kinds of silk ; that of the radii not 

 adhesive, that of the circles extremely viscid ''. The 

 cause of this difference, Avhich, when it is considered 

 that both sorts of silk proceed from the same instru- 

 ment, is truly wonderful, may be readily perceived. If 

 you examine a newly formed net with a microscope, 

 you will find that the threads composing the outline 

 and the radii are simple, those of the circles closely 

 studded with minute dew-like globules, which from the 

 elasticity of the thread are easily separable from each 

 other. That these are in fact globules of viscid gum, 

 is proved by their adhering to the finger and retaining 

 dust thrown upon the net, while the unadhesive radii 

 and exterior threads remain unsoiled. It is these 

 g'ummed threads alone which retain the insects that fly 

 into the net ; and as they lose their vii^cid properties 

 by the action of the air, it is necessary that they should 

 be frequently renewed. 



Ill this renewal, as above hinted, the geometrical 

 spiders are constantly regulated by the future proba- 

 ble state of the atmosphere, of which they have such a 



^ May not (he spinners mrntioncd by LeeuAvenhoeJv (sec above p. 405^ 

 note) be peculiar (o the rctiary spiders, and furnish this viscid thread ? 



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