The head is small compared with the abdomen, and is conical in shape; a comb of teeth is found sometimes on the cheek, or on the lower edge of the head. Eyes maybe present or absent. The head is provided with short antennae lodged in definite grooves. The mouth is furnished with appendages, maxillæ and palps, which conceal the other parts.
The thorax is composed of three segments, which are quite independent. Each consists of a dorsal arc carrying one or more belts of bristles. In some species the pronotum, or tergum of the first thoracic segment, carries a comb on its posterior edge.
The three pairs of legs are composed of a number of segments, the coxa being especially long and broad. The number and character of the bristles of the joints of the legs are used for distinguishing species.
{{smaller|The abdomen is composed of ten segments; on the ninth the tergum is in a great part occupied by a pitted sensory plate called the pygidium. In the male the sides of the tergum form large claspers. A large bristle or bristles project over and beyond the pygidium on the seventh segment, and are known as antepygidial bristles. There is a large and complex penis.
The female flea is larger than the male. The curved receptaculum seminis is a conspicuous object in the female.
The eggs are dropped by the female casually, and hatch in three or four days in summer time.
The larva lives in dust, is an active footless maggot, of a whitish colour, and is sparsely hairy. When full grown it spins a cocoon and pupates. The duration of the pupal stage depends on the temperature.
