Aedes vexans(Meigen) is a mosquito important to man in areas of low topographic relief in inland USA. Sources are both flood plains and upland depressions. Choice of flood plains as oviposition sites is affected by nature of vegetative canopy, moisture of the soil, plant detritus, frequency of flooding, and changes in the surface created by degree of siltation. Included are figures showing topographic relief, vegetative cover, and a dispersion diagram of eggs at a site typical of a wooded flood plain.