Evidence of population-level lateralized behaviour in giant water bugs, Belostoma flumineum Say (Heteroptera: Belostomatidae): T-maze turning is left biased.

Lateralized behaviour occurs in diverse animals, but relatively few studies examine the phenomenon in invertebrates. Here we report a population-level left turn bias in the giant water bug Belostoma flumineum Say (Heteroptera: Belostomatidae) in an underwater T-maze. Individuals made significantly more left turns than right turns, including when they were naïve and first introduced to the maze. Water bugs also showed significantly longer runs of consecutive left turns than right turns (i.e. LLLLL). The length of these runs, however, did not increase with experience in the maze, suggesting that the effect is not the result of learning. There were also no differences in turning bias between male and female water bugs. The proximate mechanism(s) underlying the left turn bias is unknown, but directional cues in the environment were eliminated by rotating the maze 180 degrees between experiments, suggesting the mechanism(s) is endogenous. To our knowledge this is the first study of lateralized behaviour in the Heteroptera or in a swimming invertebrate animal.