Fleas are small (length 1–4 mm) and wingless, with laterally compressed bodies composed of a blunt head, compact thorax and a relatively large rounded abdomen (Figure IV.79). In colour they are usually dark brown as adults. Eyes and antennae are small, the latter being modified in males for clasping the female from below during copulation. When not extended, each antenna lies in a groove on the side of the head. This groove may be extended as a strengthening bar within the head from eye to eye (e.g. in Pulex). Ventrally the head bears a series of appendages for sensory and feeding functions: paired maxillary palps at the front, slender epipharynx and paired maxillary laciniae form the proboscis, with basal stipes and paired labial palps posteriorly.

Within the thorax, the oesophagus leads to a crop or proventriculus with a constriction before the capacious stomach in the abdomen. Patches of strongly barbed spines protrude into the …