Fleas are characteristic parasites of birds and mammals. Occurrences of fleas on reptiles are accidental (e.g. Tillyard, 1926; Dunnet & Mardon, 1974), although they are able to digest blood of these hosts (Belokopytova et al., 1983; Vashchenok, 1988). Accidentally, fleas are able to feed even on haemolymph of ticks (Bilyalov et al., 1989). In this chapter, I address general patterns of distribution of fleas within the two classes of higher vertebrates.

Avian and mammalian hosts

The majority of fleas parasitize mammals (more than 94% of species: Vashchenok, 1988; Beaucournu et al., 2005), whereas their association with birds is much less frequent. Analysing host associations of 1951 flea species, Medvedev (1997a, b) found that fleas were recorded on 16 mammalian and 21 avian orders. Furthermore, 1835 of the 1951 species analysed were harboured by 1606 mammalian hosts, whereas only 214 species were recorded on 543 bird hosts. Among the latter, only 60 species (about 3% of the total number of flea species) can be considered as specific bird parasites (Medvedev, 1997a, b).

The number of flea–mammal associations compared with flea–bird associations suggests that fleas are mainly parasites of mammals. Parasitism on birds is, thus, secondary, and fleas parasitic on birds are commonly thought to have originated from fleas parasitic on mammals, with this switch occurring at least 16 times during the siphonapteran evolution (Hopkins, 1957; Holland, 1964).