1972] 
Fergus son — Hypochilus thorelli 
187 
had already built a web. The remains of the first female were di- 
rectly under the other’s web, but there was no evidence of damage 
to the web, so I do not know if the first female became entangled 
or was attacked on the guy lines. 
fVeb junction. The circular sheet of silk laid down on the sub- 
strate serves as an attachment point for the lampshade, and provides 
an anchor point for the spider’s last pair of legs during prey capture. 
The lampshade, containing sticky cribellate silk, is the actual prey 
trap. In addition, the lampshade serves as a protective retreat for 
the spider. 
The support and frame lines in H. thorelli webs function chiefly 
in support of the lampshade. They are too far apart to form an 
efficient prey trap, but may help deflect flying insects into the lamp- 
shade. These lines also serve to signal the approach of a potential 
predator (see Defensive Behavior below). The tangle of threads 
serves to support and anchor the lampshade. A secondary function 
of the tangle is to warn of potential predators. Although prey do 
become briefly caught in the tangle, H. thorelli does not attack them 
there. 
The web of Hypochilus is not as efficient as a two-dimensional orb 
web (in terms of effective area covered per quantity of silk), but 
it has the advantage over such strictly aerial or other strictly ground 
webs of being able to capture both crawling and flying arthropods. 
The two most abundant prey (see above) were tipulids (flying 
arthropods) and opilionids (crawling ones). Crawling arthropods 
— ants, daddy-longlegs, cave crickets, and spiders — comprised 47.5% 
of the 40 prey remains I collected. These ground arthropods prob- 
ably encounter the base of the lampshade while crawling on the rock 
surface. The flaring of the lampshade enables it to capture these 
prey when they struggle and fall after contacting the lampshade 
base. Thus the lampshade is able to intercept movements that are 
either perpendicular to the substrate or parallel to it. 
Since it builds an aerial web and does not use silk either to over- 
come or secure prey, Shear (1970) placed Hypochilus between 
steps 2 and 3 in the scheme of spider prey-capture evolution pro- 
posed by Eberhard ( 1967) : 
1. No web is spun, prey subdued by biting. 
2. Ground web spun, prey subdued by biting. 
3. Aerial web spun, prey subdued by biting and wrapped to pre- 
vent loss during subsequent attacks. 
4. Aerial web spun, prey subdued by biting and wrapping. 
5. Aerial web spun, prey subdued by wrapping only. 
