Vision is needed to avoid a moving mock-spider.

<p>The avoidance of the artificial predator is measured as the mean % time spent in the middle zone adjacent to the central cage. (a) The presence of an immobile mock-spider in the central cage significantly reduced the % time in the middle zone. (b) Canton-S flies are placed in the arena with either a centrally located mock-spider or a blackened stir bar. The avoidance of the middle zone by Canton-S is then measured with these objects immobile (still) or rotating (mobile). The movement of the mock spider and the stir bar generate a significantly greater avoidance of the middle zone than the still objects. The avoidance of the moving mock spider is even greater than the moving stir bar. (c) The blind <i>norpA</i>^<i>7</i> mutants do not avoid the moving mock spider, suggesting a visual detection of the moving mock-spider is required for this avoidance response. The middle point of each box plot represents the median, while upper and lower box display the 3^rd and 2^nd quartile respectively. The whiskers show the 90% confidence intervals. Groups with different letters situated above the column are significantly different from each other.