1973] 
Benforado & Kistler — - Araneus diadematus 
97 
Another important factor influencing differential growth is the 
initial weight of the animal. Variations in initial weights within a 
family are generally retained during the course of development. Al- 
though several possible reasons for different initial weights within a 
family have been given by others, the authors are reluctant to offer 
any explanations. 
In an orb web weaving spider such as Araneus diadematus the 
amount of food available to the animal is roughly equivalent to the 
number of prey which become entrapped in the web. The number 
of prey entrapped in the web is in turn determined by a number of 
variables such as web-site, size and fine structure of the web, and 
frequency of web building. Thus, it can be seen that the interaction 
of the variables resulting in differential size and growth is complex 
and can be divided into those factors which influence the amount of 
food available to the spider and those factors which influence the 
spider’s use of the food available to it. 
Repeated attempts have been made to explain web characteristics 
in terms of characteristics of the individual spider (Peters, 1936). 
More common, however, has been the notation of changes in the 
form of the orb web during the life of the spider (Tilquin, 1942; 
Savory, 1952) and the attempt to relate these changes to changes in 
the animal (Witt and Baum, i960; Witt, 1963; Reed et al.> 1969). 
Because influencing factors vary concurrently, it is frequently diffi- 
cult to assess the causes of changes in the form of the web. 
In our experiment we attempted to isolate the effect of one vari- 
able (weight) while minimizing the effect of a variable which nor- 
mally changes concurrently (time). All animals used hatched on 
the same date, however, one group (the heavy-fed) gained consid- 
erable weight over the period measured. The web changes accom- 
panying these weight increases are summarized in Table 1. Be- 
cause all of the animals were hatched on the same date, we conclude 
that increases in web size are due to differences in size of the ani- 
mals resulting from differential feeding rather than differences in 
age. If appetite were a factor influencing web size, it would appear 
that the hungrier, light-fed animals would build a larger web in 
an attempt to catch more food ; however, this is not the case. 
The relationship between food and the web of a spider is a deli- 
cate one. Without food, the spider’s web-building ability diminishes, 
but without a web there is no food (Peakall, 1968). Thus, like a 
businessman, the spider faces the law of diminishing returns. It 
appears that the hungry spider chooses to conserve its resources 
