Animals engaged in a complex task are often unable to allocate enough attention to a second concurrent task. We tested the hypothesis that cerebral lateralization is advantageous because it enables separate and parallel information processing and allows for a more efficient performance of concurrent cognitive tasks. Lateralized and nonlateralized (NL) female Girardinus falcatus, obtained through a selective breeding experiment, were compared in a situation requiring sharing attention between two simultaneous tasks, retrieving food items scattered on the surface, and avoiding unsolicited male mating attempts. In the presence of a sexually harassing male, lateralized females were significantly more efficient than NL females in retrieving food, while no difference between these groups was found in control experiments in which the male was absent and subjects were not required to share attention between foraging and vigilance. Lateralized females showed a negligible decrease in foraging rate while attending the additional task, suggesting that they may be able to partition the two processes in different parts of the brain.