This chapter considers the unusual nature of the British and Irish butterfly fauna and illustrate, even for such relatively small islands, how environmental gradients have affected their ranges, distributions and changes in geography over very short periods of time.

In this chapter, as a first step, a brief overview of all European islands is presented. These present an island biogeography context for the butterfly faunas of the British mainland and Ireland, the two micro-continents, which act as key sources of species for the host of surrounding satellite...