Why do lice live in hair? - briefly
Lice inhabit hair because it supplies a concealed, stable habitat that keeps them close to the scalp’s blood supply, which they need for nourishment. The strands also serve as a secure platform for laying eggs and transferring between hosts.
Why do lice live in hair? - in detail
Lice are obligate ectoparasites that have evolved to exploit the human scalp as a stable habitat. Their small, flattened bodies and clawed legs enable them to grasp individual hair shafts securely, preventing dislodgement by movement or grooming.
The scalp provides a constant temperature around 33–35 °C and a humid microclimate that prevents desiccation. These conditions are essential for the metabolic processes of both adult insects and developing nymphs, which lack efficient water‑conserving mechanisms.
Blood is the sole source of nutrition for lice. By residing within the hair layer, they remain in immediate proximity to the scalp’s rich capillary network, allowing rapid piercing of the skin to obtain meals. This close access reduces the energy expenditure required to locate hosts compared with free‑living insects.
Hair also offers physical protection. The dense filamentous cover shields lice from mechanical removal, ultraviolet radiation, and many chemical agents. Their coloration and size render them difficult to detect against the dark background of the hair, enhancing survival.
Reproductive success is tied to the hair environment. Female lice lay eggs (nits) on the shaft about 1 cm from the scalp, where the temperature supports embryonic development. The adhesive cement used for egg attachment is specifically adapted to bind to keratin, ensuring that eggs remain in place until hatching.
Evolution has refined sensory structures on the antennae to detect heat and carbon dioxide gradients emanating from the scalp. These cues guide lice toward optimal feeding sites and facilitate host localization after hatching.
Control measures must address these adaptations: disrupting the temperature and humidity balance, mechanically removing hair‑bound insects, or applying agents capable of penetrating the protective hair layer and reaching the insects’ attachment points.