28 o 
Psyche 
[December 
contained stabilimenta. The original stabilimentum discovered at 
Arraijan was in a functional web and differed in detail from those 
found in skeleton webs. No stabilimenta of this type were encoun- 
tered during the census. We photographed the first-found stabili- 
mentum and one of the type found in skeleton webs and also col- 
lected several of the latter on black paper to analyse in detail. The 
accompanying photographs were made without coating the web to 
enhance its visibility since this could have obscured the detail of the 
stabilimenta by rendering structural members differentially more 
conspicuous than in the natural state. Web photography was ac- 
complished by using two flash units, one placed at right angles to 
the web and one discharging along the plane of the web from below. 
Figure i shows the stabilimentum in the complete web. The 
immature female was ca. 17mm in length and occupied a web ap- 
proximately 29cm in height (between upper and lower foundation 
threads). The web was in a shaded location surrounded by bushes 
and had a dense and complex barrier web dorsal to the spider (below 
the sloping main sheet) and a second less dense barrier web above 
the web, ventral to the spider. The zig-zags of stabilimentum silk 
were laid down across three inter-radial gaps and in the lower part 
also followed a branched radius, but were mainly concentrated 
between two radii. The whole structure, of golden ribbon silk, 
formed a somewhat imperfect perpendicular stabilimentum, quite 
dense over 22mm of its length, and about 33mm in total length. 
As can be seen from the figure, the stabilimentum extended from the 
hub region into the viscid spiral zone. 
The stabilimenta found in skeleton webs all consisted of much 
longer structures in which silk was deposited between much more 
widely spaced radii with the attachment points more widely dis- 
persed on the structural elements. Figure 2 shows a section of one 
such stabilimentum in which stabilimentum silk was deposited en- 
tirely on a single radius for part of the length of the structure. All 
these stabilimenta were relatively inconspicuous and could have been 
overlooked in casual examination of the webs. One skeleton web 
stabilimentum that we collected had zig-zags of multi-strand silk 
extending over seven inter-radial spaces and was 30mm wide (maxi- 
mum) and over 75mm long. 
The structure and function of skeleton webs 
Several species of araneid spiders that we have studied cease to 
build complete webs at some stage and rest for one or more days on 
skeleton webs. We noted this phenomenon, without explanation, in 
