168 



PROCEEDINGS OF THE ACADEMY OF 



[1881. 



The second mode of operation resembles that of the Triangle 

 spider, Ilyptiotes cavata^ Ilentz, which has been so admirably 

 described by Wilder, and which I have very frequently and fully 

 observed in the suburbs of Philadelphia and throughout Pennsyl- 

 vania. It is at this point that the habit of our Ra}^ spider becomes 

 particularly interesting. The Triangle spider makes a triangular 

 web, which is in fact an orb sector, composed with unvarying 

 regularit}' of four spirally crossed radii converging upon a single 

 line T (fig. 6, a). Upon this line the spider hangs back downward, 

 grasping it with all her feet, and having a portion of the line, SI 

 (fig. 6, b), rolled up slack, between her two hind, or sometimes, 



Fig. 6.— Triangle spider hanging upon taut snare, a, Spider in position. SI, Ball ol 

 slack-line, b, Enlarged figure of spider, showing the mode of grasping the line. 



apparently, her fore and hind feet. Thus the forward and back 

 parts of the trap-line are taut, while the intermediate part is slack. 

 The spiral parts of the snare are also taut. When the web is 

 struck by an insect, the spider suddenly releases her hind feet, 

 the slack line sharply uncoils, the spider shoots forward, the whole 

 web relaxes, as at fig. T, and the spiral lines are thrown around 

 the insect. This is repeated several times before the prey is 

 seized. 



