How do head lice bite? - briefly
Head lice grasp a hair strand and employ short, toothed mandibles to puncture the scalp’s outer layer, drawing a minute quantity of blood. Feeding is intermittent and often produces mild itching or a localized rash.
How do head lice bite? - in detail
Head lice (Pediculus humanus capitis) attach to the scalp with three short legs that grasp hair shafts. Their mouthparts consist of a slender, needle‑like mandible and a pair of maxillae that form a piercing apparatus. When a louse locates a blood vessel near the skin surface, it inserts the mandible into the epidermis, creating a tiny puncture approximately 0.2 mm in diameter. Saliva containing anticoagulant proteins is injected simultaneously, preventing clot formation and facilitating continuous blood flow.
The feeding cycle proceeds as follows:
- Detection: Sensory receptors on the louse’s antennae sense heat and carbon dioxide, directing the insect toward a suitable site.
- Penetration: The mandible pierces the stratum corneum, reaching the superficial dermal capillaries.
- Salivation: Anticoagulant compounds in the saliva maintain fluidity of the blood pool.
- Ingestion: The louse draws up to 0.8 µL of blood per feeding episode, lasting 5–10 minutes.
- Withdrawal: After engorgement, the mouthparts retract, leaving a microscopic wound that heals quickly.
Repeated bites trigger a localized immune response. The saliva’s proteins act as allergens, prompting histamine release and resulting in the characteristic itching and erythema. Over time, the cumulative effect of multiple feeding sites may cause secondary skin irritation or infection if the scalp is scratched.
Understanding the precise mechanics of louse feeding informs effective treatment strategies, such as agents that block the mandibular action or neutralize salivary anticoagulants, thereby disrupting the parasite’s ability to obtain nourishment.