Magnetic heading (direction the spider’s ventrum faced) and web inclination (degree of slant from the vertical) in Argiope trifasciata Forska°l, a diurnal orb-weaving spider, were studied at a coastal site in southern California for nine weeks in fall 1999. Throughout the study, A. trifasciata largely occupied east-west oriented webs with their venters facing south and southwest. Mean magnetic heading was unaffected by ambient temperature extremes. Inclination levels varied from week to week over an approximately 58 range. However, these changes followed no discernible pattern and were independent both of the sun’s decrease in maximum altitude during the course of the study and of magnetic heading. Since the ventrum of A. trifasciata is dark, the consistent southern orientation exhibited by spiders at our study site suggests that they sought to maximize solar radiation in an attempt to gain heat. In addition, the east-west, facing-the-sun orientation of webs at this site places them parallel to the prevailing western breezes, minimizing their exposure to wind disturbance. As for inclination, it is unclear what factors may be influencing the degree of slant in A. trifasciata webs and further study will be needed to ascertain what they might be.
Ramirez, M. G., E. A. Wall & M. Medina. (2003) Web orientation of the banded garden spider Argiope trifasciata (Araneae, Araneidae) in a California coastal population. Journal of Arachnology 31: 405-411.