The latitudinal patterns of the phylogenetic, functional and numerical interaction specificity (PIS, FIS and NIS, respectively) of fleas and mammals in their interaction networks, from 4 biogeographic realms, were investigated at the intraspecific, interspecific and community levels to understand whether the spatial variation of interaction specificity followed the predictions of a latitudinal specialization gradient. In fleas, no latitudinal pattern of PIS was detected. Flea FIS varied with latitude in all realms at the intraspecific level and in 2 realms at the interspecific and community levels. Latitudinal trends in NIS were detected in all realms (except Neotropics) at the intraspecific level and in the Old World realms at both higher levels. In hosts, PIS varied with latitude in the Afrotropics and the Nearctic at the intraspecific level and in the Afrotropics at the interspecific and community levels. FIS demonstrated a latitudinal trend in the Nearctic at the intraspecific level and in the Palearctic at the community level. Relationships between latitude and NIS were found in all realms (except Neotropics) at the intraspecific level and in the Old World realms at the interspecific and community levels. The directions of the latitudinal pattern of the same specificity facet could be positive or negative. They differed between fleas and hosts, realms and organizational levels. The occurrence and direction of the latitudinal specialization gradient are explained by the combined actions of evolutionary, historical and ecological factors. Pooling data from regions with different biogeographical histories and landscape structures, for a macroecological analysis, may produce spurious results.