Egg-laying behaviour and selection of oviposition sites, coupled with any subsequent redistribution of egg-masses through drift and active dispersal of first instar larvae, are primarily responsible for determining patterns of larval distribution. It is therefore both logical and convenient that they should be considered in combination. The relative importance of each factor, of course, varies between species. All may be significant in species that deposit their egg-masses on to the surface of lakes and rivers, whereas oviposition behaviour alone determines the distribution of species that colonize certain specialized, patchy habitats such as phytotelmata or cattle dung.