The introduction of new pathogens and disease vectors has been recognized as a major threat to Galapagos Island biodiversity. Here I focus on mosquito species of the Galapagos archipelago, using population genetic and phylogenetic data to understand their historical and current population dynamics. I show that two mosquito species found in the archipelago have very different historical and contemporary evolutionary histories: one species, Aedes taeniorhynchus, naturally colonized the archipelago 200,000yrs ago and is now found widely in the islands, having adapted and spread to a range of different habitats. It has also changed its feeding-behaviour and now frequently feeds on reptiles in addition to mammals, unlike the continental progenitor populat ions. These properties potentially make Aedes taeniorhynchus a key bridge-vector in the archipelago for any new invading mosquito borne diseases. In contrast, I show that Culex quinquefasciatus, a major vector of diseases such as West Nile virus and avian malaria, has been introduced on multiple occasions since 1985 via human transportation networks and that its distribution and movement in the archipelago depend greatly on human activities. These two species might play an important role in the introduction and spread of new diseases in the Galapagos archipelago.