Anti-wetting wing surface characteristics of a water bug, Diplonychus annulatus

Diplonychus annulatus sp. (family Belostomidae and order Hemipetra) is an aquatic water bug, adapted to ponds and wetlands. Commonly referred to as toe-biters or electric-light bugs, both the nymph and the adults prey on other invertebrates in the water. In search of both food and mates, the adults frequently fly between water bodies, leading to an amphibious lifestyle. It is likely that because of such a lifestyle, they have evolved structures on their wings that enable them to be dry and be able to fly. In this paper, we report the anti-wetting property of the fore and hind wings. We show that wings, have intricately designed hierarchical structures of setae, microtrichia, and a "micro-architectured well" interspersed with club-like projections. The wings were extremely superhydrophobic with water contact angle ranging between 160⁰ to 170⁰. FTIR analysis of the wings indicated the presence of hydrophobic groups. Thus, due to both, the intricate surface features as well as possibly the low surface energy due to the hydrophobic groups on the wings, the water bug can maintain a high degree of dryness in its wings. We discuss these findings in the context of how wing adaptations contribute to the insect's ability to thrive in its amphibious lifestyle.