Why do sucking lice live only on mammals?

Sucking lice (suborder Anoplura) are highly specialized ectoparasites that feed exclusively on the blood and tissue fluids of mammals. Their restriction to mammals is primarily driven by their extreme host specificity and specialized physiological adaptations.12

These insects have evolved to thrive within the specific environment of a host's pelage, relying on body heat and the physical structure of hairs for survival. For instance, some mammalian lice can only attach their eggs to hairs of a specific diameter. Because they are unable to survive for long periods away from their host, they are biologically dependent on the unique conditions provided by the mammalian body.2

Furthermore, the relationship between sucking lice and their hosts is often characterized by parallel evolution, where the parasite has diverged and evolved alongside its host. This long-term co-evolution has resulted in chemical and physical compatibilities that make the louse dependent on the specific host species or closely related groups. While secondary infestations on new hosts can occur, the louse's survival remains contingent upon finding a host that meets its precise nutritional and habitat requirements.132