Haematophagy has evolved independently in different insect groups. This has resulted in the development of different kinds of adaptations (e.g. suitable mouthparts as well as alterations in the gut anatomy and in digestive enzyme composition). At the same time, insects have acquired different levels of adaptation to blood-sucking habits. One of the most interesting examples is the co-evolution of sucking lice (Anoplura) with their hosts. Human head and body lice, Pediculus humanus capitis De Geer, 1767 and Pediculus humanus humanus Linnaeus, 1758, are highly host- and anatomic-region-specific ectoparasites. They spend their entire lives on the host, ingesting small blood meals, several times per day. To date, several genes encoding digestive protease and proteolytic activities have been identified. The blood is stored in the anterior distensible region of the midgut, where genes encoding serine endopeptidases are highly expressed. Likewise, in the narrow posterior region of the midgut, the high-level expression of genes encoding exopeptidases has been documented. Symbiotic microorganisms inhabiting the mycetome complete the deficient nutrition of human lice. This review focuses on the digestion habits of the best-investigated taxon of human lice P. h. humanus in relation to other blood-sucking insects.