1980] 
Coddington & Valerio — Wendilgarda Spiders 
97 
a water film on a leaf, and is completely free of the stream, it is only 
attached to the film, and not to the leaf itself. In this way one can 
observe the attachment point more closely; even under 20X magnifi¬ 
cation there are no discernible accessory lines leading away from the 
immediate locus of the thread. An increase in the tension on the sticky 
thread results in an increase in the distortion of the water film at the 
site of the thread junction. The water film can be pulled upward by 
the thread into the shape of a cone, strongly suggesting that there is 
some sort of interaction between the silk and the water film. If the 
sticky thread is now coated with cornstarch, there is a noticeable 
accumulation at the thread-water junction, covering essentially the 
area of the water film distorted by the tension in the sticky line. If a 
similar piece of non-sticky Wendilgarda silk is lowered into water and 
coated with cornstarch, no such accumulation is seen. 
Web tension. Apparently the vertical sticky lines are under more 
tension than can be explained by the action of water surface tension 
on a simple inert filament. We make this conclusion based on the 
following observations. 
1. Except in web sites where the surficial flow rate exceeds about 
0.2 m/sec, the sticky lines pass straight into the stream, approxi¬ 
mately normal to the water surface. As any fisherman has 
observed, inert lines with little drag on them always sag down¬ 
stream in a current. The angle of the sag depends upon the drag 
and the current. Although increased flow rates do move the point 
of attachment of a sticky line downstream with respect to the 
horizontal line, the path described by the sticky line is essentially 
straight with no observable sag. This suggests that it behaves like 
elastic filament under a tension whose magnitude far exceeds its 
weight per unit length. 
2. If non-sticky segments of Wendilgarda silk are immersed in the 
water film of the same web site from which they were collected, 
they behave like inert fibers: they point downstream, there is an 
observable sag in the aerial portion of the line, and it requires no 
noticeable force to pull them out of the water. 
3. If the horizontal line of a Wendilgarda web is held at the point 
of attachment of a sticky line, and slowly raised until the water- 
thread junction fails, the sticky thread elongates 50% to 100% of its 
original length. Also, if the water-silk junction is broken artifi¬ 
cially, and the sticky line allowed to hang under the stress of its 
own weight, it is typically only half the length it assumed when in 
