SURFACE-SKIMMING STONEFLIES - A POSSIBLE INTERMEDIATE STAGE IN INSECTFLIGHT EVOLUTION

Insect wings appear to have evolved from gills used by aquatic forms f or ventilation and swimming, yet the nature of intermediate stages rem ains a mystery. Here a form of nonflying aerodynamic locomotion used b y aquatic insects is described, called surface skimming, in which thru st is provided by wing frapping while continuous contact with the wate r removes the need for total aerodynamic weight support. Stoneflies su rface skim with wing areas and muscle power output severely reduced, w hich indicates that surface skimming could have been an effective form of locomotion for ancestral aquatic insects with small protowings and low muscle power output.