1979 ] Christenson, Wenzl & Legum — Nephila clavipes 139 
To determine if there was a seasonal variation in individual egg 
weight, number of eggs per clutch, and total egg clutch weight, we 
collected and examined 63 egg sacs in 1977 and 93 in 1978. Egg 
clutches were removed from mid-August through early December. 
In 1977 weekly samples were taken from a thoroughly examined 
1500 sq mt area within the hardwood forest. Only those egg sacs 
that appeared to contain yellow eggs were collected. In 1978 weekly 
samples were taken from a thoroughly examined 600 sq mt area of 
the hardwood forest bordering a cleared drainage ditch. Half of the 
egg sacs found in the latter area were randomly chosen for removal 
and examination, and half for observation throughout the winter in 
the field. The egg sacs brought into the laboratory were placed in 
Petri dishes, the inside covers of which were mist sprayed with water 
every other day. A normal day-night cycle and a temperature of 
about 22° C were maintained in the laboratory. About four days 
after collection the silk was removed from the sac, and the egg mass 
was weighed. The delay in handling was designed to minimize dam¬ 
age to the eggs, since they are particularly fragile for a few days after 
oviposition. The egg mass was carefully broken apart and the eggs 
counted. Within two days of counting a random sample of 10 yellow 
eggs was drawn from each clutch; each egg was weighed separately 
on a Mettler analytic balance. 
Results 
Field observations revealed a seasonal variation in the emergence 
of spiderlings; they were less likely to emerge from egg sacs laid later 
in the season (Table 1). The numbers in Table 1 and under twig 
Table 1. Percentage of egg sacs from which no spiderlings emerged in the spring 
according to the trimester of the season in which the egg sac was formed. Each 
trimester represents about six weeks. Estimated numbers of failures are in paren¬ 
theses; see text for explanation of estimate. Trimester effect analyzed by Chi square 
test; data were collapsed across years. 1 
Trimester: 
%— Early 
%— Mid 
%—Late 
1975 
1976 
1977 
1978 
26.6(20.8 of 78) 
29.8(26.6 of 89) 
35.3(16.6 of 47) 
31.3(16.6 of 53) 
60.5(29.0 of 48) 
94.5(44.4 of 47) 
10.0( 1.7 of 17) 
42.0( 8.4 of 20) 
72.3( 8.7 of 12) 
100.0(10.0 of 10) 
78.4( 7.8 of 10) 
75.0( 6.0 of 8) 
1 X 2 2 = 62.45, p < .001 
