140 
Psyche 
[June-September 
breakage in Table 2 are estimates based upon the fact that 84.2% (16 
of 19) of the egg sacs that were found after falling to the ground 
failed to produce spiderlings. The three successful clutches fell 
within one month prior to the normal time of spring emergence. We 
estimated the number of failures by multiplying the number of egg 
sacs that fell by .84. We feel this is a correct estimate since several 
clutches that were never found fell shortly before the normal time of 
emergence. 
One major cause of mortality was egg inviability, distinguished by 
the hard and blackened nature of the eggs. There was a seasonal 
variation in inviability; it caused most of the late but few of the early 
season failures (Table 2). Its exact causes are not known, although 
fungus was not found on inviable eggs and no parasites emerged 
Table 2. Causes of spiderling failure to emerge from the egg sac according to the 
trimester of the season in which the egg sac was formed. Actual numbers for the egg 
inviability and miscellaneous categories, and the estimates for twig breakage are in 
parentheses. 1 
Causes of Failure 
Year and Trimester: 
% Egg Inviability 2 
%Twig Breakage 
% Misc. 3 
1975 
Early 
19.3 ( 4) 
56.6 (11.8) 
24.1 (5) 
Mid 
55.1 (16) 
17.4 ( 5.0) 
27.5 (8) 
Late 
57.6 ( 5) 
19.4 ( 1.7) 
23.0 (2) 
1976 
Early 
48.9 (13) 
28.5 ( 7.6) 
22.6 (6) 
Mid 
72.1 (32) 
18.9 ( 8.4) 
9.0 (4) 
Late 
80.0 ( 8) 
0 
20.0 (2) 
1977 
Early 
0 
75.9 (12.6) 
24.1 (4) 
Mid 
0 
100.0 ( 1.7) 
0 
Late 
89.3 ( 7) 
10.7 ( .8) 
0 
1978 
Early 
24.1 ( 4) 
75.9 (12.6) 
— 
Mid 
59.8 ( 5) 
3.4 ( 4 ) 
— 
Late 
100.0 ( 6) 
0 
0 
■See text for explanation of estimate. 
includes the cases in which the twig fell after the eggs hatched. 
3 Misc. includes immobility (3), loss of leaf canopy (3), damage to the silk 
surrounding the eggs (2), fungus (10), and predation (7). The 1978 egg sacs were not 
observed as often as those in previous years; therefore, causes under this category can 
not be assessed with the accuracy possible for the previous years. 
