1979] Christenson, Wenzl & Legum — Nephila clavipes 141 
from samples brought into the laboratory. There was also seasonal 
variation in the second major cause of mortality, twig breakage; 
early season sacs fell more frequently than those formed later (Table 
2). Twig breakage resulted in the eggs falling to the ground, and 
subsequently rotting or being preyed upon. No seasonal variation, 
however, was noted in the frequency of failures caused by immobil¬ 
ity of the egg sac after lodging on a branch, loss of the leaf canopy 
over the eggs, damage to the silk covering the eggs, fungus, or 
predation (Table 2). 
Seasonal variation in certain egg parameters were also noted. 
Individual egg weight in clutches laid early in the season was signifi¬ 
cantly greater than in those laid later (Table 3). The same was true 
for total egg weight. The early 1978 clutches also contained signifi¬ 
cantly more eggs (Table 3), but no significant relationship was 
found between individual egg weight and number within a clutch. 
The Pearson correlations between these two parameters in 1977 and 
1978 were r= +.068 F li42 = .20, p > .05 and r = +.202 (F,. 82 = 3.44, 
p > .05), respectively. 
Discussion 
Seasonal variation in spiderling emergence may be due, in part, to 
climatic factors. Clutches laid early in the season are exposed for a 
longer period of time to wind and rain which, in turn, may increase 
the likelihood of those clutches falling to the ground. Moreover, the 
early part of the egg laying season coincides with the peak of the 
hurricane and rainy season which may cause a higher frequency of 
twig breakage, the major cause of failure among early season 
clutches. 
Climatic factors may also contribute to the increase in egg invia¬ 
bility of clutches laid later in the season. For example, the cooler 
temperatures later in the season may significantly delay hatching, 
similar to that found in temperate N. edulis (Austin and Anderson, 
1978). Christenson and Wenzl (manuscript submitted) have shown 
that N. clavipes eggs are particularly vulnerable to some causes of 
mortality during the three week period prior to hatching. Cooler 
temperatures may also reduce the amount of prey available to adult 
females, thereby hampering egg production. 
The seasonal variation in inviability could also be due, in part, to 
the maturation of the adult. Some of the late season clutches are 
probably the later ones produced by given females. Horner and 
