418 FOOD OF INSECTS. 



silk proceed from the same instrument, is truly wonder- 

 ful, 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 glo- 

 bules 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 gummed threads alone which retain the in- 

 sects that fly into the net ; and as they lose their viscid 

 properties by the action of the air, it is necessary that 

 they should be frequently renewed. 



In this renewal, as above hinted, the geometrical spi- 

 ders are constantly regulated by the future probable 

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

 perception, that M. Q. D'Isjonval, to whom we are in- 

 debted for the fact, has proposed them as most accurate 

 barometers. He asserts that if the weather be about to 

 be variable, wet and stormy, the main threads which sup- 

 port the net will be certainly short ; but if fine settled 

 weather be on the point of commencing, these threads 

 will be as invariably very long*. Without going the 

 length with M. D'Isjonval of deeming his discoveries 

 important enough to regulate the march of armies, or 

 the sailing of fleets, or of proposing that the first appear- 

 ance of these barometrical spiders in spring should be 

 announced by the sound of trumpet, I have reason to 

 suppose from my own observations that his statements 

 * Brez, La Flore des Imectophilcs, 129. 



