THE STABILIMENTA OF NEPHILA CLA PIPES 
AND THE ORIGINS OF 
STABILIMENTUM-BUILDING IN ARANEIDS* 
By Michael H. Robinson and Barbara C. Robinson 
Smithsonian Tropical Research Institute, 
P.O. Box 2072, Balboa, Canal Zone 
Structures of multi-strand (ribbon) silk are built into the webs 
of certain araneid and uloborid spiders. These devices are widely 
known as stabilimenta (following Simon 1895). Marples (1969) 
has objected to the functional connotations of the term and has 
called such structures decorations. However, we feel that there is 
no point in abandoning a term that has acquired a. designatory value 
largely independent of functional implications. 
The stabilimenta built by araneids differ, from species to species, 
in form, complexity and disposition within the web. There can also 
be differences between the stabilimenta built by different develop- 
mental stages within the same species. Some species build disc 
stabilimenta at one stage in the life cycle and linear stabilimenta at 
another (almost always later) stage. Despite these differences (ex- 
amples in Robinson & Robinson 1970, Ewer 1972, general discussion 
with references in Kaston 1964) araneid stabilimenta have construc- 
tional features in common. With the exception noted below, all the 
stabilimenta that have been described consist purely of silk that is 
laid down between structural elements of the web in a zig-zag 
manner. In linear stabilimenta, the subject of this paper, the zig- 
zags bridge the gap between adjacent radii. An exception to this 
common constructional feature occurs in the stabilimenta built by 
some species of Cyclosa in which the devices incorporate discarded 
remnants of prey and other debris, and may also contain egg sacs. 
These stabilimenta are perhaps best regarded as a special case and 
could be described as ‘composite.’ 
As far as we are aware, there has been no record of stabilimentum 
building by spiders of the genus Nephila prior to its discovery in 
Nephila maculata (Fabricius) by Robinson & Robinson (1973). 
These authors found that N. maculata builds a perpendicular linear 
stabilimentum in very rare instances. The structure is built only by 
immature females and shares the constructional features described 
* Manuscript received by the editor November 4, 1973. 
277 
