Biological classification aims to group and categorise biological entities that share some unifying characteristics. Identification is a precise term describing the allocation of an unknown specimen to a predefined group. In any system, it is important that it is easy to retrieve information, and this is best done if similar animals are grouped together. There are two basic stages in systematics: first, recognition of biologically operational units, which are the basic units of any classification; and secondly, the ordering of these units into higher categories or levels. Mosquitoes of the different genera have different kinds of eggs. Those of anophelines are characterised by having floats on the side. Those of culicines are laid on the water surface together and form a ‘raft’ visible to the naked eye. The concept of the ecological niche is that each species occupies a unique ‘hyperspace’ that involves biological and environmental characteristics.