Insects are the pre-eminent form of metazoan life on land. The class Insecta contains over three-quarters of a million described species. Estimates for the total number of extant species vary between 1 and 10 million, and it has been calculated that as many as 1019 individual insects are alive at any given instant (McGavin, 2001). That gives about 200 million for each man, woman and child on Earth! It is estimated that there are 14 000 species of insects from five orders that feed on blood (Adams, 1999) but, thankfully, only 300 to 400 species regularly attract our attention. These blood-sucking insects are of immense importance to humanity.

Humans evolved in a world already stocked with blood-sucking insects. From their earliest days insects would have annoyed them with their bites and sickened them with the parasites they transmitted. As humans evolved from hunters to herders, blood-sucking insects had a further impact on their wellbeing by lowering the productivity of their animals. It is reasonable to assume that, because of their annoyance value, humanity has been in battle with blood-sucking insects from the very beginning. In recent years this battle has intensified because of an increasing intolerance of the discomfort they cause, our fuller understanding of their role in disease transmission and the demand for greater agricultural productivity. But despite considerable advances in our knowledge of the insects and improvements in the weapons we have to use against them, there is still no sign of an eventual winner in this age-old battle.