We studied mosquito faunas of four wetlands from northern to southern Sweden by trapping female mosquitoes in June, July, and August. A total of 52,298 individuals comprising 32 species in five genera were identified. The number of species increased from 10 and 12 in the two northern wetlands, to 16 in the central Sweden study area, to 24 in the wetland in southern Sweden. For a further characterization of mosquito fauna diversity, we organized all species recorded from Sweden into 14 functional groups based on biological and life history characteristics. The number of groups increased from three in the two northern study areas, to eight in central Sweden, and 13 in the southernmost study area. All functional groups present at one site were also present at the sites located farther south. Most successful species were univoltine, respiring from the water surface, laying their eggs on soil, overwintering in the egg stage, preferring forested or partly forested habitats, and having mammals as hosts for blood meals. The mosquito faunas of the two northern study areas were similar and lacked several of the functional groups occurring further south. The mosquito fauna of the study area in central Sweden included species feeding on birds and with overwintering larvae. In the southernmost study area, 13 out of 14 functional groups were found, indicating a large variety of habitats. Our results demonstrated a southward increase in the number of both mosquito species and functional groups in forested wetlands.