The eggs of mosquitoes are brown or blackish and are laid singly or in rafts (1) on the water surface of diverse types of water collections; (2) on the undersides of floating vegetation, to which they are 'glued'; and (3) on wet mud, leaf litter, other damp substrates near the edge of water. In the latter case they usually hatch when flooded.
In nature, usually 4 to 5 ovipositions occur, each with 30-500 eggs. The site of oviposition is species-specifically chosen according to water chemistry and a circadian rhythm.
In the tropics, eggs hatch within 1-2 days, in cooler climates this process might take 1-2 weeks. Some mosquito eggs (e.g. Aedes and Ochlerotatus species) can withstand desiccation and may remain viable for months or years in a dry state.