The world flea fauna includes about 2000 species, belonging, according to our classification (Medvedev, 1994), to 18 families. In database of our analytical information system PARHOST1, host-parasite relations of 1951 species of the Siphonaptera were analyzed, of which 1835 flea species were found on 1606 mammal species and 214 flea species on 543 bird species.
Thus, the ratio of parasite and host (mammal and bird) species is 1.1:1 and 1:2.5, respectively. At the level of genera this ratio is 1:2.1 and 1:4.2 for mammals and birds, respectively. At the level of families - 1:5.1 and 1:7.4, respectively.