FOOD OF INSECTS. 405 



tion. Of the probable accuracy of this calculation you 

 may any clay in summer convince yourself, by taking 

 one of the large field spiders (Epeira Diadema), and 

 after pressing its abdomen against a leaf or other sub- 

 stance, so as to attach the threads to the surface the 

 same preliminary step which the spider adopts in spin- 

 ning drawing it gradually to a small distance. You 

 will plainly perceive that the proper thread of the spider 

 is formed of four smaller threads, and these again of 

 threads so fine and numerous, that there cannot be fewer 

 than a thousand issue from each spinner ; and if you 

 pursue your researches with the microscope, you will 

 find that precisely the same takes place in the minutest 

 species that spins. You will inquire what can be the end 

 of machinery so complex ? One probable reason is, that 

 it was necessary for drying the gum sufficiently to form 

 a tenacious line, that an extensive surface should be ex- 

 posed to the air ; which is admirably effected by dividing 

 it at its exit from the abdomen into such numerous 

 threads. But the chief cause, perhaps, is the occasion 

 (hereafter to be adverted to) which the spider sometimes 

 has to employ its threads in their finer and unconnected 

 state before they unite to form a single one. The spider 

 is gifted by her Creator with the power of closing the 

 orifices of the spinners at pleasure, and can thus, in 

 dropping from a height by her line, stop her progress at 

 any point of her descent: and, according to Lister 3 , she 

 is also able to retract her threads within the abdomen; but 

 this is doubted, and with apparent reason, by De Geer b . 

 The only other instruments employed by the spider 

 in weaving are her feet, with the claws of which she 

 11 Hist. Anbn. Ang. p. 8. h De Geer, vii. 189. 



