Mosquitos and their larvae form a major part of many killifishes diet, and are eagerly accepted in the aquarium. There are around 3000 species throughout the world, all of which require water for sucessful reproduction. In areas with only seasonal bodies of water, insect larvae can form an almost exclusive part of a killifishes diet (eg Nothobranchius species in parts of Africa) and as such attempts have been made to use killifish as a form of mosquito control in these areas. Unfortunately this solution is not proven effective (see below).
Mosquitos are a major vector for Malaria (300-500 million cases each year worldwide, 90% in Africa) and other diseases, so it is not wise to encourage mosquitos unless you live in a 'safe' part of the world (the UK is fine at the moment).
The mosquito life cycle consists of four stages, all of which can easily be observed anywhere where mosquitos occur. The first is as egg rafts (figs 1a and 1b). These are typically laid on the water surface, though they can withstand cold and dry conditions; many species survive the winter in unhatched rafts.
The larval stage is next. These larvae grow quickly feeding on microorganisms and plant matter, though they always return to the surface as they breathe air from the surface through a specialised tube (fig 2). Larvae are often killed by placing a thin layer of oil on the waters surface to prevent breathing
The next stage is the familiar 'comma' shaped pupae (fig 3). This stage lasts for only a couple days, in which time they do not feed. At this stage they should only be fed to fish in limited numbers as uneaten individuals will pupate rapidly within the warmth of a fish house and fill your home with mosquitos!
The last stage is the emerged adult mosquito. It is only the female mosquitos that bite and drink blood, and some will not lay more eggs until they have had a blood feed.
Mosquitos are most readily taken by killifish in the larval stage. Many keepers will collect rafts throughout the summer, store them in cool conditions and hatch them when live food is less readily available. Fish that have not been fed them may take a while to recognise them as food (particularly if they are used to food being on the bottom rather than the surface).
Rafts are usual laid on still stagnant water, with rotting vegetation and/or animal matter. This can be very shallow; rafts are often layed in a few centimeters of water. Clear clean rainwater is usually unsuitable as it contains insufficient microorganisms. The greatest yields occur when a mouse/slug etc falls into the water, drowns and slowly decays.