Aedes aegypti, on Grand Bahama Island, is restricted to certain western towns, whereas A. bahamensis is more generally distributed. During 14 years of observation, the range of A. Aegypti has extended 8 km and now includes the major tourist centre. Relocation of discarded automobile tires is an important mechanism for such spread. We suggest that the presence of A. bahamensis restrains colonization by A. aegypti, and thereby helps to protect human populations from A. aegypti-borne disease.