1987] 
Hodge — Residence time of Micrathena 
369 
similar to the area in the present study. The distribution of residence 
times in these deciduous forest areas is almost identical, and both 
are significantly different from that predicted by the negative 
exponential. An interpretation of these distributions may be as 
follows. If each successive interval of nonperformance of a behavior 
depletes the animal’s energy reserves, performance of the behavior 
(i.e., web site relocation) becomes more beneficial as the time 
elapsed since the last performance increases (Fagan & Young 1978). 
This applies to M. gracilis in that if a spider at a certain web site 
experiences a reduction in prey capture due to web destruction 
and/or low feeding rates, then the time between relocations (time 
spent at that site) results in a certain depletion of the spider’s energy 
reserves. This may culminate in some energy-related cue, perhaps a 
threshold hunger level, which stimulates the spider to perform the 
behavior of web site relocation. 
Summary 
This study examined the factors influencing web site residence 
time of the orb weaving spider Micrathena gracilis. Residence time 
at a particular site was used as an indicator of microhabitat quality. 
When spider residence times were compared to a negative exponen- 
tial distribution, the distribution of observed residence times was 
significantly different from that expected from a random movement 
hypothesis. The relative contributions of prey consumption, web 
destruction, and sun-exposure (heat stress) were monitored by 
hourly census checks of marked spiders over a 22 day period. 
Thirty-four of 36 web site relocations were preceded by a day of 
either zero or one feeding observation, and/or web destruction by 
wind or rain. There were few observations of sun-exposure accom- 
panied by thermoregulatory posturing, and of these, few were fol- 
lowed by web site relocation. Web destruction and low prey levels 
are suggested as contributing to a threshold hunger level which 
stimulates spiders to seek new web sites. 
Acknowledgments 
I would like to thank Drs. R. W. Matthews and J. O. Howell for 
providing the financial support and the opportunity to conduct this 
study. Drs. J. Arnold and G. Morrison provided statistical advice 
and Drs. G. W. Uetz and A. L. Rypstra offered valuable editorial 
