REACTIONS OF ORB-WEAVING SPIDER TO VIBRATIONS OF WEB. 319 



this Epeira seems to be. especially expert. When a fly strikes a 

 web it often goes through, breaking out one or two spiral segments. 

 If, however, it does not break through it hangs for a second, buzz- 

 ing, then breaks one or two of the sticky strands and flies away. 

 A fly seldom entangles itself to such an extent that it cannot get 







free inside of five seconds. A successful spider then must reach 

 the fly in less than two or three seconds after it strikes the web. 

 The actual capture of the fly is accomplished usually either by 

 biting the fly and stunning it or by winding it with web. The 

 entangled fly may be left where it struck or may be torn from the 

 web, and carried attached to one of the spider's hind feet to the 

 center of the web where it is thoroughly chewed and its liquid 

 parts swallowed. 



The apparatus used to produce rhythmic vibrations consisted 

 of three tuning forks and an electric vibrator. One fork had 

 a vibration rate of 100 double vibrations per second, another a 

 rate of about 487 and the third was an adjustable fork with a 

 large range of vibration rates but with very limited amplitude. 

 The electric vibrator was a modified electric door bell in which the 

 clapper was replaced by a long grass straw. The number of 

 vibrations produced by this instrument could be varied to some 

 extent by changing the tension of a spring and a regulator screw, 

 while the amplitude of the vibration varied with the length of 

 straw used. The vibration rate of the vibrator was obtained 

 by comparing a tracing made by it on a sheet of blackened 

 paper on a revolving drum with a simultaneous record made by 

 the tuning fork giving 100 double vibrations per second. The 

 electric vibrator was found to be more effective than a fork because 

 it gave vibrations of equal intensity, i, e., it did not run down. 

 It had also another advantage in that it could be controlled by a 

 switch held in the hand and could be operated at a distance from 

 the operator. A stop watch was used to measure the time elaps- 

 ing between the beginning of the stimulus and the arrival of the 

 spider at the place where the straw touched the web. 



III. EXPERIMENTS. 



i. Experiments Using Rhythmic Vibrations. 

 When the vibrator straw is placed against one of the spiral 

 strands or against one of the radii and caused to vibrate the spider 



