1977] 
Tietjen — Dragline- Following by Spiders 
175 
Male L. punctulata and primed male L. rabida may be able to 
extract directional information from the female dragline, though 
it is unlikely that a pheromone concentration gradient could pro- 
vide the directional information since the pheromone remains active 
over long periods of time. Examination of female L. rabida silk 
under a light microscope (450X) as well as scanning electron micro- 
scope inspection of female L. punctulata silk (1000X) indicate no 
evidence of structural features on the dragline which could provide 
directional information to males. 
Spiders are able to detect slight changes in web tension through 
vibration receptors during prey capture, web building, and court- 
ship (Robinson, 1969; Walcott, 1969; Witt, 1975). Such variations 
in tension, related to the direction in which the dragline was laid, 
could provide directional information to dragline-following males. 
If present, the tension differential may be related to the structure 
of the attachment disk by which the silk is fixed to a substratum. 
As the dragline enters the attachment disk it is tightly wound, 
whereas the silk leaving the attachment disk is composed of single 
threads which later join and wind to form the dragline. Single silk 
threads leaving an attachment disk would be expected to damp 
transients produced along the line more readily than a complete 
dragline entering an attachment disk. If this were the case, drag- 
line-following toward the pole with the higher resonant frequency 
would constitute movement in the direction the silk was laid (Tiet- 
jen, unpub. data). Such a system would require that males im- 
mobilize a portion of the dragline, perhaps with a palp, while 
plucking on either side of the fixed portion. Male spiders en- 
countering a female line often wipe the dorsal surface of each palp 
alternately over the silk and often pluck at the silk with the first 
legs as they swivel their bodies along a short length of the trail. 
This behavior may represent both a sampling for female phero- 
mone and a testing for differential mechanical properties of the 
line related to the direction in which it was laid. 
Unprimed male L. rabida did not exhibit a polarity in dragline- 
following, but a positive correlation between courtship latency and 
total distance followed was observed. The above correlation indi- 
cates that unprimed males probably have a lower threshold for 
chemical cues than do primed males. If unprimed males are at- 
tending more to chemical cues, they would be less likely to follow 
