Invasive species pose a threat to global biodiversity by displacing native species from their habitats. Biological invasions can also be facilitated by global warming and urbanization, which can benefit invasives that have higher thermal tolerances or adaptability. The Brown Widow (Latrodectus geometricus) is an invasive spider from southern Africa that has displaced native black widow species in urban environments across the globe. We hypothesized that L. geometricus outcompetes native congeners because of its greater tolerance to the higher temperatures associated with urban environments in San Juan, Argentina, and Northridge and Palmdale, California, USA. We (1) estimated the relative abundance of native and invasive widows along transects spanning urban to natural environments, and (2) compared the thermal physiologies (critical thermal maximum, CTmax, and climbing performance from 20–40 °C) of native and the invasive species on both continents. We found that Brown Widows were more abundant in urban and transitional habitats in San Juan and Northridge, CA, yet Western Black Widows (L. hesperus) were more abundant in all habitats in Palmdale. There were no differences in CTmax among species from the same locality, although there were differences among locations. Finally, there were no differences in thermal performance among widow species or locations. Our data suggest the invasive success of Brown Widow in urban areas cannot solely be attributed to advantages in thermal physiology and future studies should focus on interspecific interactions.