Throughout time, shifts in species ranges caused by changes in climate and environment have created isolated populations of animals, presenting them with a suite of genetic and behavioural challenges. In modern times, human-mediated transport of novel species and the fragmentation of habitats lead to the creation of numerous isolated populations. Here, we use the Aesculapian snake (Zamenis longissimus) as a model species which has a broad natural distribution and multiple introduced populations. We investigate the behaviour of this snake in its introduced range in North Wales using radiotelemetry of wild snakes. Our results suggest a reliance on human features of their semi-rural landscape. Using whole-genome sequencing, we compare the genetic structure and health of multiple native populations of Aesculapian snakes with the introduced populations in Wales and England. Then, we infer the biogeographic history of Aesculapian snake populations. We find the population in Wales to be of uncertain, possibly mixed ancestry, and the population in London to have stemmed from an introduction of Italian specimens. Finally, we examine a long-isolated population natural population of rinkhals, a venomous snake from Zimbabwe. Using museum DNA approaches, we demonstrate evidence of speciation resulting from this isolation, and formally describe the Nyanga rinkhals (Hemachatus nyangensis).