1987] 
Hodge — Residence time of Micrathena 
367 
Table 1. Number of spiders relocating after exposure to various environmental 
factors. 
Environmental 
Factor 
Spider 
Relocation 
% of total 
relocations 
No spider 
relocation 
Exposure to 
direct sunlight 
3 
8% 
45 
Thermoregulatory 
posture 
1 
3% 
3 
Courtship attempts 
3 
8% 
15 
Web destruction 
alone 
5 
15% 
39 
Low prey levels 
alone 
16 
47% 
63 
Both low prey and 
web destruction* 
13 
38% 
82 
*Chi-square test for independence indicates no differential influence of web destruc- 
tion alone, low prey levels alone, or a combination of these factors on relocation; 
X 2 = 2.16, p> 0.50. 
significantly correlated with the animal’s energy gain, and therefore 
its fitness. Though a correlation between energy gain and fitness has 
not been shown for M. gracilis, it has been for many spider species 
(Deevey 1949; Turnbull 1962, 1965; Miyashita 1969; Hagstrum 
1970; Kessler 1973; Greenstone 1978; Kajak 1967, 1978; Wise 1975, 
1983). Morse & Fritz (1982) found that female crab spiders gain 7/8 
of their biomass during the adult stage, which was the stage of most 
of the spiders observed in this study. Since biomass accumulation is 
crucial for egg production, it seems that web site residence time 
should be related to the energetic costs and benefits of moving 
versus staying. Factors such as web destruction (reduction of feed- 
ing time; cost of rebuilding) or low feeding rates may lead to a 
threshold hunger level which stimulates the spider to move. 
The fact that 33 of 34 web relocations were preceeded by a day of 
low prey levels (0-1 feeding observations/ day) and/or web destruc- 
tion seems strong evidence that these factors are involved in the 
decision to move. However, most occurrences of low feeding rates 
and/or web destruction did not result in relocation (Table 1). The 
only conclusions that can be made from these data are that, 
although these two factors are almost always associated with web 
relocation, their occurrence alone is not enough to cause the spider 
