Confirmation that tension-dependent cues do not guide sticky spiral construction in Micrathena duodecimspinosa, and the probable reason why

Sticky spiral construction behavior in orb-weaving spiders is strikingly flexible: 10 to 16 different cues influence the hundreds of decisions that a spider makes while building the sticky spiral in an orb. Several variables that are influenced by radial tensions, including the frequencies and amplitudes of vibrations and the extensibility and tensions of the radii, have been repeatedly mentioned as possible cues guiding sticky spiral placement. Nevertheless, previous studies have suggested that radius tensions do not affect sticky spiral spacing. These tests were complicated, however, by the tight correlations between variables due to the highly regular geometry of orbs, possible context-dependent variation in the use of cues, and the intrinsic difficulty of demonstrating the absence of an effect. Greater certainty regarding tension-dependent cues is crucial for understanding the cues guiding orb construction, so this study extends these experiments, examining the effects of both increasing and decreasing radius tension, and of different sequences and magnitudes of changes. The results confirm previous findings: changes in radius tensions did not influence sticky spiral spacing decisions in consistent ways and generally failed to produce statistically significant effects. I argue that the likely reason why spiders do not use tension-dependent variables to guide sticky spiral placement is that such cues are unreliable because the spider's own weight substantially alters the tensions on nearby web lines in complex and variable ways.