1980] Horton — Stabilimenta of Orb Weaving Spiders 15 
webs within the aviary during the night and early morning. Three 
spiders were then selected—one having no web, one having a web 
without a stabilimentum and one having a complete web. The 
remaining spiders and their webs were removed. If none of the spiders 
had produced a web without a stabilimentum one web was randomly 
selected and its stabilimentum removed with a hot needle. The “non¬ 
web” spider was a spider which had suspended itself on a few strands 
in the normal resting position. 
In other cases the spiders used in the experiments had built their 
webs within aluminum frames (50X50X5 cm) with glass panels in the 
front and back which were removed prior to placing the frames in the 
aviaries. During an experiment, two of the frames contained spiders 
in webs, one with, and one without a stabilimentum. The third frame 
contained a spider which had been killed by freezing and was 
suspended by thread in the characteristic resting position in the center 
of the frame. The frames were placed in random order side-by-side on 
a table within the aviary. The data obtained from the experiments 
using spiders in frames were combined with data from spiders which 
had constructed their webs within the aviary. 
The second set of experiments was performed using pen and ink 
drawings of orb webs. These drawings were executed in white ink on a 
brown background, and were approximately the size of a normal, 
adult Argiope web. The drawings were suspended within the 
aluminum spider frames, using the same three web conditions used in 
the previous experiment. Crickets were suspended by thread in the 
position that would normally be occupied by the spider. The blue jays 
used were trained to recognize crickets as food, and were naive with 
respect to spiders and spider webs. 
Once the three webs or web drawings were in place, a blue jay was 
released into the aviary. Capture sequence, capture time, and the 
behaviors exhibited by the blue jays and the spiders were recorded. 
An attempt to capture a spider which resulted in only a portion being 
taken was scored as a capture. 
The null hypothesis in the experiment outlined above was that the 
web and stabilimentum would have no effect on predation. The 
alternative hypothesis was that these structures would inhibit 
predation. If the null hypothesis were valid, the capture sequence 
(i.e., which spider/cricket was taken first, second, third) would have 
been random. A nonrandom sequence, in which the non-web spider 
tended to be taken first, the partial web spider second, and the full 
web spider last, would support the alternate hypothesis. 
