The β-diversity of fleas parasitic on small mammals in 45 regions of the Palearctic was partitioned into species [species contributions to β-diversity (SCBD)] and site ( = assemblage) contributions [local contributions to β-diversity (LCBD)]. We asked what are the factors affecting SCBD and LCBD and tested whether (a) variation in ecological, morphological, life history and geographic traits of fleas can predict SCBD and (b) variation in flea and host community metrics, off-host environmental factors, host species composition of flea assemblages can predict LCBD. We used spatial variables to describe geographic distribution of flea assemblages with various LCBD values. SCBD significantly increased with an increase in abundance and a decrease in phylogenetic host specificity of a flea as well as with size and latitude of its geographic range, but was not associated with any morphological/life history trait. LCBD of flea assemblages did not depend on either flea or host species richness or environmental predictors, but was significantly affected by compositional uniqueness ( = LCBD) of regional host assemblages and variables describing their species composition. In addition, variation in LCBD was also explained by broad-to-moderate-scale spatial variables. We conclude that SCBD of fleas could be predicted via their ecological and geographic traits, whereas LCBD of their assemblages could be predicted via host composition.