1980] 
Eberhard — Bolas Spider 
159 
about 25% of the wet weight of prey captured into eggs. These M. 
dizzydeani captured an average of 15.7 moths per sac; and the 
average wet weights of moths and sacs were 59.2 (N=9) and 331 mg 
N=l) respectively. This gives 331 mg of eggs resulting from 931 mg of 
prey, or 35.6% of prey weight being converted into eggs. These figures 
are only approximate, especially in light of the small sample of egg 
sac weights and the underestimates of prey captured. They are close 
enough to the value used by Eberhard (1979) to encourage belief that 
the calculations made there are not wildly wrong. 
Egg Sac Construction 
Spiders ceased predatory activity as much as 24 hours before 
ovipositing. Egg sac initiation was seen three times, always between 
0:00 and T.50. As illustrated in Fig. 16 there were three recognizable 
stages First the spider made a disc of greyish-white fluffy silk 
suspended from one side (Fig. 16a). She enlarged this by adding silk 
to the sides and bottom with a stereotyped dabbing movement: the 
spinnerets were touched to the edge of the disc, then legs IV lifted the 
disc up and away, then brought it back down; this cycle was repeated 
over and over, with several threads being drawn each time. After 
about five minutes of this the spider held the disc against her ventral 
surface where it received the ball of yellow eggs which slowly emerged 
(Fig. 16b,c). The oviposition took approximately five more minutes, 
and when the ball was complete the spider pulled the sides of the disc 
around it and fastened them together with more dabbing movements 
so that the eggs were sewn into a cradle of fluff. She then made more 
fluff by holding the suspension line with one leg I and slowly 
treadmilling on the ball, pulling her abdomen away after each 
attachment so that it “bobbed” back and forth. This then gave way to 
further treadmilling without the bobbing movement but instead 
quick (2-4/sec.) side to side dabs with the abdomen, and the sac 
began to acquire a smooth outline (Fig. 16d). Within 20 minutes after 
the eggs had emerged they were no longer visible except for a yellow 
glow inside the ever-thickening walls when they were illuminated. 
About 15 minutes later, as the spider continued her treadmilling, the 
sac began to darken. The final product (Fig. 16e) was somewhat 
variable with respect to color and details of form, but was very similar 
to the sacs of M. cornigera and M. bisaccata (Gertsch 1947, 1955). A 
thick stem which spread into a plane at the top supported a nearly 
spherical sac which had in some cases small excrescences near the 
