Thirteen transverse latitudinal transects are used to examine the biogeographic pattern of the peninsula effect on 341 species of Florida carabid beetles. In this fauna, 278 species are grouped to be of temperate affinity or origin, 28 of tropical affinity or origin, and 35 are endemic to Florida; 39 of the species are flightless. The species are ecologically grouped as riparian, hygrophile, halophile, mesophile, subxerophile, arboricole, and endogean. Both the total fauna and the temperate group show a peninsula effect, that is, a decrease in species richness from peninsula base to tip. The tropical group shows an inverse peninsula effect: their species richness decreases toward the base. The endemic group displays a much different pattern, with maximum richness at the middle of the peninsula, a possible reflection of former Tertiary or Quaternary islands as centers of isolation and speciation. Over-water dispersal has been important: 61 species crossed the water gap between Florida and West Indies; 36 temperate species moved from Florida into the West Indies; 25 West Indian (tropical) species have crossed the water gap into Florida (69% of these are preadapted hygrophilic, riparian, and halophile species). Species movements between Florida and the West Indies were probably more prevalent at times of Pleistocene low sea levels, when these lands were larger in area and closer to each other. The Gulf Coastal Plain has provided an avenue for carabid movement to and from Florida and the continental Neotropics with 44 species occurring in both areas, and 70% of these are preadapted hygrophilic, riparian, and halophilic species.