ENGINEERING SKILL OF SPIDERS. 



225 



radiating supports seized the margins. These structures, moditied as they 

 doubtless were by their environment and in a measure thus compelled to 

 their final form, evidently show considerable skill in adapting spinningwork 

 to circumstances. 



There is no doubt that in the ordinary operations of snare making and 

 nest building, the Labyrinth spider continually brings into play certain 

 l)rinciples of oi)eration which may be properly designated by the 



tLTiii engineering. For example, in looking at Labyrinthea work- 



Labyrinth 



Snare ^^^^ ^P ^^^ maze of crossed lines in which her domicile is liung, 



one is continually impressed with the fact tiiat she so balances 

 and adjusts the lines as they are successively spun out, that the whole 

 spinningwork is as 

 well suited to its 

 purposes as is the 

 complex scaffolding- 

 used by human car- 

 penters in building 

 a house. I cannot 

 conceive in what 

 manner the spider 

 perceives the vari- 

 ous inequalities, on 

 this side or that, 

 which require spe- 

 cial treatment in 

 the way of staying, 

 tightening, adding," 

 etc. Peril aps her 

 sense of touch is 

 so delicate that her 

 perception of these 



necessities is accurate enough to enable her to construct her intricate snare 

 so as to attain precisely the same results as would have been reached had 

 she been guided by an engineering intention from the very first. 



Again, Labyrinthea is in the habit of roofing her silken tent with a 

 leaf. Sometimes the leaf is used in lieu of the tent, and again the tent 

 is woven inside of the concavity of the leaf. In order to ob- 

 serve the moile of treatment I once dropped a curled leaf into 

 a newly made snare of this spider. She at once perceived its presence by 

 the agitation of the maze, ran to it, and appeared innnediately to perceive 

 its value. She fastened to it here and there a line, as though to preserve 

 it from falling farther and thus damaging lier snare. Slie then ran to 

 the stem, attached a strong thread to it, and clambered out u[)on her silken 

 trestle for the distance of two inches, and then fastened her line, leaving 



"'i' Himill!ll!l!ll"'ll 



mummmmmmmvimmMmmMmmmmmmiMimmmi 



'//'rl/J/N.' 



Fig. 213. Globular structure of young Theridium tepidariorum. 



Roofing. 



