How do lice bite on the head? - briefly
Lice pierce the scalp with needle‑like mouthparts (stylets) and draw blood while injecting saliva that contains anticoagulants. The resulting bite produces a localized itching sensation.
How do lice bite on the head? - in detail
Head lice (Pediculus humanus capitis) attach to the scalp using specialized claws that grasp hair shafts near the scalp surface. Once secured, the insect positions its head close to the skin to access a blood vessel. The mouthparts consist of a slender, curved stylet formed by the maxillae and mandibles, which act together as a piercing‑sucking apparatus.
The feeding sequence proceeds as follows:
- Anchoring – The louse uses its three‑toed claws to lock onto a hair strand, preventing displacement.
- Penetration – The stylet pierces the stratum corneum and epidermis, reaching the dermal capillary network.
- Saliva injection – The insect injects a small amount of anticoagulant saliva that contains proteins preventing clot formation and reducing host irritation.
- Blood uptake – Negative pressure generated by the louse’s foregut draws blood into the alimentary canal. The volume per bite is minute, typically 0.5–1 µL.
- Withdrawal – After engorgement, the stylet retracts and the louse resumes movement along the hair shaft.
The entire bite lasts a few seconds, after which the host may experience a pruritic reaction due to the immune response to the saliva proteins. Repeated feeding leads to cumulative irritation and potential secondary infection if the skin is broken.
Key physiological adaptations that enable this process include:
- Sharp, serrated stylet for efficient epidermal penetration.
- Anticoagulant enzymes (e.g., apyrase) that maintain blood flow.
- Sensory receptors on the head that detect temperature and carbon dioxide, guiding the louse to optimal feeding sites.
Understanding these mechanisms informs effective control strategies, such as targeting the mouthparts with insecticidal agents or disrupting the lice’s ability to cling to hair.