86 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



made with a rapidity which often prevents the eye from following the 

 motions of the foot and spinnerets. 



When the innermost spiral is reached the araiiead swings or strides to 

 the hub, takes up her position head downward and bites out the flossy 

 guidon, which she takes within her mouth. 1 Whether or not it is finally 

 rejected I cannot say, but it is certainly retained for some time, and I 

 believe is dissolved within her mouth, and swallowed. 



What becomes of the unbeaded scaffold lines which the spider uses for 

 weaving in her system of beaded spirals ? They are not seen among the 

 concentrics when the orb is finished, and the secret of their dis- 

 appearance is only to be unfolded by watching the architect as 

 Removed s ^ e P rocee ds with her work. It will thus be found that as she 

 spins her way from the outer margin toward the centre she 

 bites off her scaffolding and permits it to drop away, rolling it up usually 

 within her jaws. It has served her purpose by giving her footing while 

 engaged in forming the essential part of her structure, and when she 

 needs it no longer she removes it, precisely as the mason when "point- 

 ing" his stonework takes down his wooden scaffold as he works from the 

 top toward the bottom of his wall. I have observed this process repeat- 

 edly, as others have done. 2 Mr. Emerton 3 speaks of "a few turns in the 

 centre " apparently confounding what I have called the " notched zone " 

 with the special scaffolding, as his figure also shows. The latter is 

 not simply a continuation of the former, but is rather an independent and 

 permanent part of the orb, having a wholly different use and is separate- 

 ly spun. Blackwall says that the " innermost circle " of the spiral scaffold 

 is permitted to remain; but my observations, on the contrary, are that all 

 the concentrics are removed and the beaded spirals carried to the very 

 margin of the free zone. Possibly the habit is not invariable in its 

 details ; and on the whole presents a good example of intelligent exercise 

 of the spinning function. 



II. 



The efficiency of an orbweb for the capture of prey depends chiefly 



upon its viscidity and strength. The former quality pertains to the spiral 



lines which differ from the other parts of the web in being 



Spiral covered at close intervals with minute viscid beads. To these 



Tjf^flifTS 



the value of the snare as an instrument is chiefly due, for they 

 adhere to and melt upon the wings, limbs, and hairs on the bodies of 

 insects that strike the web, and thus fatally entangle them. Rennie has 



1 Kirby and Spence, Introduction to Entomology, page 413, are quite correct in their allusion 

 to this fact, but the biting away of the cotton like tuft is not necessarily accompanied by 

 the opening up of the hub. Blackwall suggested the probably tme reason why the central 

 space is without viscid beads. 



2 Blackwall, op. cit., page 183. 



3 Emerton, American Naturalist, ii., 478 ; Packard's Guide, page 646 ; Structure and Habits 

 of Spiders, page 64. 



