34 
Psyche 
[March 
TABLE 2. 
Barrier webs and stabilimenta of A. aurantia 1 
N 
Mean number of 
bands ± S.E. 
Barrier 
webs 
Early & mid-instars (study area) 
61 
4.789 ± 0.218 
9 
Penultimate & adult $ ’s (study area) 
28 
2.429 ± 0.196 
0 
Older adult 9 ’s (study area) 
29 
1.828 ± 0.100 
0 
Older adult $ ’s (Knox Co., Tenn.) 
50 
1.740 ± 0.085 
0 
1 Thin “patch” was not assigned a value and thus was not used in calcu- 
lations. 
female webs in my study area to those of a population near Stock 
Creek Boat Dock in Knox County, Tenn. The results of a t-test 
showed no significant difference (p<0.05) in the number of bands 
in these two populations. It is interesting that Reed, et al., (1969) 
found “no obvious pattern or change in complexity” in laboratory- 
reared A. ciurantia. Whether this difference is due to selection pres- 
sures or possibly some cue(s) existing in field situations that do not 
exist in the laboratory is not known. 
The stabilimenta of A. aurantla can conceal the spider. Conceal- 
ment of the spider’s state (especially when molting) is probably 
advantageous. Both Argiope species molt at the hub during the day 
and are completely defenseless during this process. Concealment of 
the true size of the spider may also be a deterrent to the invertebrate 
predator since larger orb weavers can ward off and maybe even kill 
a smaller attacker. It is even possible that stabilimenta conceal attack- 
eliciting stimuli from certain predators. 
A. trifasciata constructed substantially fewer bands in their webs 
than A. aurantia (Tables 1 & 2). A Cox & Stuart test for trend 
indicated a significant increase (p<o.05) in the number of bands 
with instar of A. trifasciata (20 individuals of each instar were 
selected at random prior to testing) . These results differ from Com- 
stock (1948) who found that juvenile A . trifasciata built extensive 
disc-shaped stabilimenta. The reasons for these differences are not 
known, but I suspect that extensive use of barrier webs and the 
increase in stabilimenta bands may be related to heavy predation 
pressure by salticids. 
Stabilimenta can also function as physical shields. The heavy silk 
bands reinforce the hub and make direct penetration more difficult. 
This is readily demonstrated by forcing a. pencil or similar object 
through the hub of webs with and without such stabilimenta. 
