1980] 
Eberhard — Bolas Spider 
157 
swing. The greatest extension observed amounted to about 3.5-4 cm. 
This change was completely reversible and the recovery was evidently 
very rapid. I never noticed any elongation after swings by spiders, nor 
was I able to see any elongation when I myself swung a newly-made 
ball and looked quickly after each swing. The significance of this 
property of the ball is probably that it increases the spider’s striking 
distance while maintaining between swings the compact ball form 
which is essential for quick and accurate strikes. Such use of spring¬ 
like action is unusual if not unique in animal structures. 
In summary, it appears that the ball may function in the following 
way. The low viscosity liquid is sufficiently wet and abundant to flow 
past the moth’s scales and reach a relatively large area of the cuticle 
below. The more viscous liquid forms the actual bond to the thread 
which sustains the moth’s weight, and the thread folded inside the ball 
functions to permit quick, reversible elongations which extend the 
spider’s striking range and perhaps also serves to hold prey once it is 
hit. 
Prey 
The prey caught by a given individual of M. dizzydeani are 
relatively constant, but, as shown in Table 1, there is variation 
between individuals even at the same site. Some but not all the 
differences might be due to differences in prey abundances at 
different times of the year, although casual observations suggest that 
this was not the case. Small spiders seem to differ radically from 
larger ones in prey identity, which is expected given the relatively 
large size of the larger spiders’ prey. 
Rates of prey capture were estimated from numbers of moths 
found in sticky traps placed under four mature females’ hunting sites; 
they were certain underestimates since several times I saw a spider 
feeding on a moth in the evening but found no prey in the trap the 
next morning (probably some prey were blown clear of the traps 
when they were discarded). A total of 204 moths was found after 100 
spider hunting nights (nights dedicated to egg sac construction were 
not counted), giving an average of 1.85 moths per hunting night. 
Since the rates of egg sac production were determined for these same 
four spiders during the same period (23 sacs in 219 spider days), these 
data can be used to test the assumption on which Eberhard (1979) 
based calculations of prey capture rates—namely that spiders convert 
