A novel underside water surface‐walking behavior in larvae of Hydroporus uenoi Nakane, 1963 (Coleoptera: Dytiscidae)

Larvae of diving beetles (Coleoptera: Dytiscidae) are generally regarded as fully submerged predators that inhabit aquatic environments and occasionally surface to breathe. However, during laboratory rearing of the hydroporine species Hydroporus uenoi Nakane, 1963, we discovered a previously undocumented behavior: larvae walking upside down along the underside of the water surface. Larvae were also observed walking along the bottom and sides of the rearing cup, but the repeated occurrence of upside‐down locomotion underneath the water surface indicates that their use of the surface layer is not accidental. Our observations suggest that fine‐scale habitat segregation in dytiscid larvae may be more diverse than previously recognized. To our knowledge, this is the first report of underside surface‐walking behavior in dytiscid larvae, highlighting the need for further field and comparative studies on larval microhabitat specialization.