406 TEXT-BOOK OF ZOOLOGY 



C. Food. 



This consists chiefly of flies and gnats. Being wingless, however, it 

 is unable to pursue its prey into their own domain, the air, nor is it able 

 to capture these light-winged creatures by running. Nevertheless, means 

 must be found to get possession of its dipterous victims, and hence, like 

 the fisherman, who cannot pursue his prey in the water, the spider 

 puts up — 



1. A Net. — Let us study more closely the manner in which the spider 

 constructs this artistic contrivance, and by what structural arrangements 

 it is adapted for its work : 



(a) Method of spinning the Web. — The ■ web is always stretched 

 vertically between two supports — let us assume two tree-trunks. A 

 horizontal thread is first stretched between the two supports, strong 

 enough, and fixed sufficiently firmly, to carry the animal. This thread 

 is first glued to one of the trunks, and carried by the animal over inter- 

 vening branches (if there are such), as over a bridge, to the opposite 

 trunk, where it is pulled tight and glued fast in the same manner. If, 

 however, the two trees are separated by some intervening obstacle, e.g., 

 water or a ravine, and no connecting-bridge of branches is available, the 

 spider, after gluing the thread to one of the trunks as described before, 

 allows it to flutter freely, and to be carried by a current of air over to 

 the opposite trunk, where it adheres easily to the rough bark. 



Next a new thread is spun, and glued to suitable spots on the two 

 trunks. In this manner an irregular polygon is produced, which forms 

 the frame of the snare. Across this frame a diagonal thread is next 

 spun, and from the point of its bisection threads radiate in all directions, 

 like the spokes from the hub of a wheel. At the same time as the spokes 

 a small disc of threads disposed in circles is spun gradually around the 

 centre. By pulling at one of these threads the spider observes where an 

 additional spoke may still be required. Finally, after all the spokes have 

 been further connected by a wide spiral thread, the creature commences 

 to draw another in a narrow spiral around the centre of the web ; this 

 is the real snare thread, and is studded with permanently viscid globules 

 (see Section 2). The wheel-shaped snare is now complete, and, as a 

 finishing touch, the spider destroys the first unadhesive spiral, which 

 merely served as a bridge or ladder between the spokes. 



The material for this ingenious structure is furnished by — 



(b) Numerous large spinning glands, which lie in 



(c) The abdomen, and account for its strikingly large size. 



(d) The fluid matter from which the web is formed leaves the body 

 by six very small wart-like prominences at the end of the abdomen, the 



