REACTIONS OF ORB-WEAVING SPIDER TO VIBRATIONS OF WEB. 317 



of the female of tfcis species of remaining at the center of her web 

 for long periods of time makes it a very convenient form to study 

 in its normal surroundings. 



This species builds its web in dead branches or in the angles of 

 buildings where there is an abundance of small or medium sized 

 insects. The web usually consists of 17. 18 or 19 relatively 

 inelastic strands which radiate from a center like the spokes of a 

 wheel. These radiating strands are attached at their outer ends 

 to twigs or boards or to guys or stays which anchor several radii 

 to the support. Surrounding the center of the web is an irregular 

 network known as the hub and notched zone which serves as a 

 resting place for the inhabitant of the web. For a short space 

 outside the hub the radii are bare (the free zone) but beyond this 

 is found the viscid spiral consisting of finer strands which are 

 extremely elastic and are beaded with microscopic sticky drops 

 which serve to hold and entangle the insect prey. It is probably 

 the extreme elasticity of these spiral strands which allows them 

 to detain a strong insect without being snapped, thus giving the 

 spider time to reach the detained insect and complete its en- 

 snarement by the addition of fresh silk from the spinneretts. 

 The normal resting position of the female spider is with the head 

 directed downward and the legs spread outward on the notched 

 zone as is shown in Fig. i . The method used to obtain this pho- 

 tograph and the others following is that used by Comstock 

 ('12, p. 181). A female spider was placed on a dead branch held 

 in the neck of a bottle which was set in a tray of water. During 

 the first or second night the spider usually built a perfect web. 

 The branch was then moved to the photographing table with as 

 little disturbance as possible and placed in front of a soap box 

 painted a dull black on the inside. Arranged in this way before 

 the camera it was possible to take pictures showing the spider, 

 web, and vibrator straw, and the various positions taken by the 

 spider in the act of responding to the vibrator. 



The size of the web varies from two inches in diameter, or even 

 smaller when built by very young spiders, to eighteen inches or 

 more when built by mature females. The male builds a web 

 very much like that made by the female but as he has a roving 

 disposition one is never sure that the same individual can be 



