Selenops galapagoensis was recently synonymized with Selenops mexicanus because the types of the former did not differ from the latter in any visible way. Additionally, a large molecular analysis of the genus from North and Central America and the Caribbean that included both nuclear and mitochondrial genes showed no differences indicating two separate species. However, no specimens from the Galápagos Islands, the only place where no distributional overlap occurs between the putative species, were previously available for molecular analysis. Recently, specimens suitable for molecular data collection became available from the Galápagos, allowing us to test whether genetic differences existed between mainland and island specimens and whether molecular data supported their synonymization. We performed phylogenetic analyses of mitochondrial and nuclear DNA of newly obtained Galápagos specimens, confirmed S. mexicanus specimens, and appropriate outgroups. We found that almost all of the Galápagos specimens share identical haplotypes despite being collected from different islands in different years, and that these haplotypes are also shared with, or differ by only a few nucleotides from, mainland specimens. The genetic variation between the island and mainland specimens is much less than the genetic variation observed among other Selenops species and within S. mexicanus across its distribution. The results from the molecular data indicate that S. mexicanus was likely transported to the Galápagos Islands via humans within the past 500 years, and these data also support the synonymization of S. galapagoensis with S. mexicanus.