Hedgehog flea (Archaeopsylla erinacei), coloured scanning electron micrograph (SEM). The two structures protruding from the centre of the flea's head are sensory palps. Below these are the mouthparts, which pierce the skin to enable the flea to suck the blood of its host. Combs, known as ctenidae, at the top of the head help to anchor the flea to its host's fur. Fleas are external parasites that may carry and transmit diseases. This flea may also feed on pets and humans. Fleas only remain on their host whilst feeding.