Limb loss and specialized leg dynamics in tiny water-walking insects

Abstract

The air-water of the planets water bodies, such as ponds, lakes and streams, presents an uncertain ecological niche with predatory threats from above and below. As Microvelia move across the water surface in small ponds, they face potential injury from attacks by birds, fish, and underwater invertebrates. Thus, our study investigates the effects of losing individual or pairs of tarsi on the Microvelias ability to walk on water. Removal of both hind tarsi causes Microvelia spp. to rock their bodies (yaw) while running across the water surface at {+/-}19{degrees}, compared to {+/-}7{degrees} in non-ablated specimens. This increase in yaw, resulting from the removal of hind tarsi, indicates that Microvelia use their hind legs as rudders to regulate yaw, originating from the contralateral middle legs strokes on the waters surface through an alternating tripod gait. Ablation of the ipsilateral middle and hind tarsi disrupts directionality, making Microvelia turn in the direction of their intact limbs. This loss of directionality does not occur with the removal of contralateral middle and hind tarsi. However, Microvelia lose their ability to use the alternating tripod gait to walk for water walking on the day of contralateral ablation. Remarkably, by the next day Microvelia adapt and regain the ability to walk on water using the alternating tripod gait. Our findings elucidate the specialized leg dynamics within the alternating tripod gait of Microvelia spp., and their adaptability to tarsal loss. This research could guide the development and design strategies of small, adaptive, and resilient micro-robots that can adapt to controller malfunction or actuator damage for walking on water and terrestrial surfaces.