Insect wings are composed of thin, flexible, double-layered elastic membranes. Veins form where these layers separate, often creating campanulate cross-sections. The vein walls are also elastic structures, making the entire wing an interconnected elastic continuum. One can think of a wing membrane as a set of flexible ‘panels’ connected by flexible struts (veins). Many species of insect can fold, unfurl, and adjust the shape of their wings during flight. Although such shape control is primarily exerted by basal wing muscles, changes in wing shape are observed throughout the wing. While the potential for hydraulic contributions to this control has been long hypothesised, it remains largely unexplored. Insect veins contain hemolymph, a fluid circulated by thoracic 'wing hearts.' Hydraulic pressure has been implicated in the folding/unfolding of hindwings in beetles and other insects. It is plausible that vein rigidity could be actively controlled through pressure variations, either synchronised with wingstrokes or maintained over multiple wingbeats. We propose a novel mechanism for active wing shape control: hydraulic distortion of vein cross-sections, which exert leverage on adjacent cross-veins and membrane. Hydraulic distortion of vein cross sections can induce wing shape changes by varying relative orientation of adjacent membrane panels. This mechanism holds significant technical potential, with applications in deployable structures and micro aerial vehicle wing design. We model the vein cross-section as a cavity bounded by two elastic curves (elasticae) of different lengths, this difference captures the asymmetry of the cross-section shape. Hemolymph pressure is approximated as a differential normal pressure acting on the boundary of the cross-section. This model accounts for large deformations and sudden shape changes, such as the snap-buckling observed during wing folding and unfolding. Asymmetry, a key factor in snap-buckling, is inherent in the non-circular cross-sections of many insect veins. We explore the relationships between haemolymph pressure, vein cross-sectional geometry, wall stiffness, and resulting deformations. We formulate biomimetic design criteria for triggering wing folding/unfolding.