1980] 
Eberhard — Bo las Spider 
155 
and Gasteracantha cancriformis (Eberhard in prep.), and again 
serves to emphasize the unusually fluid nature of Mastophora’s 
adhesive. 
Spiders never discarded balls, always carefully ingesting them even 
when they accidentally stuck to their own bodies (observed three 
times) or to nearby objects (observed once—to a cardboard wind¬ 
screen held near the spider). In addition to the obvious conservation 
of nutrients which this represents, it may also be important in the 
conservation of water, since the spiders sometimes go for long 
periods without drinking and also endure high temperatures at 
exposed sites during the day (above). 
Cursory examination of balls on glass slides showed that their 
internal structure was complex, and consisted of a mass of curled or 
folded fibers which was embedded in a viscous matrix which was in 
turn surrounded by a less viscous layer (Fig. 13). More refined 
observations by R. W. Work (pers. comm.) showed that the folded 
“spring” fibers are noodle-like ribbons which are nearly rectangular 
in cross section (Fig. 15), with only slightly rounded corners and 
slight bulges on their flat sides. He reports as follows: “The 
dimensions of two samples of these fibers from Mastophora dizzy- 
deani were 10.7 X 3.4/umand 10.0 X 3.2^™. A sample from a closely 
related species from Costa Rica gave 11.4 X 4.3 /xm. They are 
possessed of axial birefringence, being of the same order of magni¬ 
tude (0.005-0.007) in planes perpendicular to both thick and thin 
axes of their cross sections. In this way they differ markedly from the 
elastomeric baselines of the sticky spirals of araneid orb webs, which 
are birefringent in neither the non-extended nor extended states. It 
follows that the bolas throwing and recovery phenomena are not 
based on elastic properties. Rather, the combination of rectangular 
cross section (typical of a steel spring), folded or sinusoidal con¬ 
figuration while at rest, and axial molecular orientation (as evidenced 
by bifrigence) is the basis of the springiness. The spring fibers are also 
different from the fibers making up the line from which the ball was 
suspended since these latter, which are also birefrigent (values 
approximated .02-.03, typical for lines from the major ampullate 
glands of other arachneids), were round (4-5 pm in diameter) as is 
typical of other spider fibers. The details of the junction between the 
bolas and the suspension line could not be resolved, although it 
appears that spring fibers may be present in the ‘bundle’ near the end 
of the line.” 
