Aquatic assassins: Proteo-transcriptomic and functional profiling of giant water bug and water scorpion venoms

Aquatic heteroptera possess highly specialized salivary venoms that they use to immobilize their prey; however, their evolutionary origins, molecular composition, and functional diversity remain poorly understood. Here, we integrate proteo-transcriptomics with biochemical analysis to compare venoms from three different ecologically important taxa: giant water bug (Lethocerus indicus), electric light bug (Diplonychus rusticus), and water scorpion (Laccotrephes maculatus). The proteo-transcriptome profiling revealed that peptidases are the dominant toxin family across all three species, establishing proteolysis as the functional axis of heteropteran venoms. Species-specific differences included a CUB-domain expansion in L. indicus, elevated lipase in D. rusticus, and abundant cytolytic components such as cystatin, serpin, and hemolysin in L. maculatus. Further functional comparative investigations revealed that the venom of L. indicus exhibited strong proteolytic and fibrinogenolytic activity, specifically degrading the Aα and γ chains of human fibrinogen. The L. maculatus venom showed the highest cytotoxicity and phospholipase activity, whereas D. rusticus venom demonstrated comparatively greater protease activity. Furthermore, coagulation assays revealed that venom from L. indicus induced the most pronounced coagulopathies, despite all three species displaying overall anticoagulant effects. These interspecific differences uncover previously unrecognized diversification in heteropteran venom strategies and suggest independent evolution of hemotoxic mechanisms in aquatic lineages. Overall, our findings establish a molecular and functional framework for understanding venom evolution in predatory water bugs and water scorpions and identify bioactive components with potential antithrombotic relevance.