THE AERIAL WEB SPINNERS 179 



air until it catches on some object; whereupon it is pulled taut. Al- 

 ternatively, the spider may fix a line, carry it, by dropping or walk- 

 ing, down one side of the area to be covered, across and up the 

 other side to the point of attachment, holding the line free of en- 

 tanglement all the time. Once the bridge line is fixed, it is strength- 

 ened by additional threads as the spider moves back and forth across 

 it. (See Text Fig. 6.) 



From some point on the bridge line the spider now drops down 

 to a lower point and fixes a plumb line to grasses, twigs, or any 

 substratum. To this plumb line the spider next attaches a third line, 

 and, holding it free, climbs back up to the bridge, along it for a 

 distance, then attaches and tightens the third thread. There is now 

 formed a triangle, its dimensions dependent upon the distance trav- 

 eled on the bridge line, whose apex points down and in which the 

 round snare can be placed. 



These foundation lines may be roughly rectangular, trapezoidal, 

 or otherwise configured, and are dependent upon the local condi- 

 tions and the habits of the species. 



Within the framework the spider now lays down the radii. 

 First it must put down a diameter line to pass through the point 

 that is to be the center of the orb. This may be accomplished by 

 dropping down from the bridge line, or by walking the diameter 

 line, held free, around the framework to the opposite point, where 

 it tightens and fixes the line. From some point on this initial diame- 

 ter line originate all the other radii of the web, each put down by 

 carrying it around to the desired attachment point over the already 

 fixed lines. According to McCook, the radii are as a rule laid alter- 

 nately on the opposite sides of the enclosed space, but there may be 

 less regularity that he supposed. The tension on the lines, no doubt 

 susceptible to testing by the spider, may well influence it in setting 

 down the radii, which are often placed with quite remarkable ac- 

 curacy to form nearly equal angles at the center, but in other cases 

 are grossly asymmetrical. 



After fixing the last radius, the spider usually goes to the point 

 where the radii converge and strengthens it by spinning a mesh of 

 lines termed the hub. A part of the hub is made while the radii are 

 being placed and stretched, and it is completed after the last one is 

 fixed. Around the hub are then spun several spiral turns, which, 

 because they are laid down and pulled to form irregular notches, 

 are termed the "notched zone"; they serve to strengthen the central 

 area and tighten the radii. The next step is to put down across the 



