Evolutionary developmental biology has provided invaluable contributions to our understanding of the relationship between genotypic and phenotypic change. Similarly, evolutionary ecology greatly advanced our understanding of the relationship between the phenotype and the environment. To fully understand the evolution of the organismal diversity, a thorough integration of these fields is required, and this remains highly challenging. Semi-aquatic insects (Heteroptera, Gerromorpha) have conquered water surfaces worldwide and represent by far the dominating group of insects in these habitats. Their well-understood ecology of adaptation constitutes the necessary foundation for integrative studies.We will dissect the developmental genetic basis of key morphological adaptations associated with the ecological transition from ground to water surfaces. A morphological character that has been critical to this transition is the evolution of hydrophobic bristles, whose density, morphology, and orientation, allow the trapping of air at the leg–water interface. A second spectacular adaptation, that followed this invasion, is the occupation of running waters by some members of the family Veliidae. This was facilitated by the evolution of a swimming fan on the tarsus of the propelling mid-legs, which greatly enhances their movement on running waters.The objective of this project is to develop a multi-level approach to study how the interplay between developmental genetic pathways and the ecological environment can drive morphological evolution. We will take full advantage of the unique foundation in terms of ecology, diversity, and technical tractability that water-walking insects offer, combined with the use of next generation sequencing along with assays of gene function and organismal fitness. This approach is a critical step forwards in evo-devo and will provide a coupling of molecular function to concrete measure of fitness associated with the phenotype.