There are about 2500 species and subspecies of fleas in about 220 genera, butonly relatively few are important pests of humans. About 94% of species bitemammals, while the remainder are parasitic on birds. Fleas occur almostworldwide, but many have a more restricted distribution; for example the genusXenopsylla, which contains important plague vectors, isconfined to the tropics and warmer parts of some temperate countries.

Medically the most important fleas are Xenopsylla species, suchas X. cheopis, which is a vector of plague(Yersinia pestis) and flea-borne murine typhus(Rickettsia typhi). Fleas in the genusCtenocephalides may be intermediate hosts of cestodes(Dipylidium caninum, Hymenolepisdiminuta). Fleas may also be vectors of tularaemia (Francisellatularensis), and the chigoe or jigger flea (Tungapenetrans) ‘burrows’ into people’s feet.

External morphology

Adult fleas are more or less oval in shape and relatively small (1–6 mm); theyare compressed laterally and vary from light to dark brown(Plate 19). Wings are absent, but there are three pairs of powerful legs, withthe hind legs specialized for jumping. The legs, and much of the body, arecovered with bristles and small spines.

The head is approximately triangular, bears a pair of conspicuous eyes (a fewspecies are eyeless), and short three-segmented more or less clubshapedantennae which lie in depressions behind the eyes. Themouthparts point downwards. In some species a row of coarse, well-developedtoothlike spines, collectively known as the genal comb or genalctenidium, is present along the bottom margin of the head (Figs. 11.1,11.2).