Insects are the pre-eminent form of metazoan life on land, with as many as 1018 individuals alive at any one instant and over three-quarters of a million species described. Although it is estimated that there are as many as 14,000 species that are blood feeders, only three to 400 species regularly attract our attention. Some of these are of immense importance to us, as vector-borne diseases still form a huge burden on both the human population and our domesticated animals.