How do lice parasitize? - briefly
Lice grasp hair shafts, insert their specialized mandibles into the epidermis, and repeatedly pierce to draw blood while injecting anticoagulant saliva. They deposit eggs (nits) on the host’s hair, ensuring a continuous supply of parasites.
How do lice parasitize? - in detail
Lice are obligate ectoparasites that depend on a host’s blood for nutrition and reproduction. Their life cycle consists of egg (nit), three nymphal stages, and adult. Each stage requires direct contact with the host’s skin or hair to obtain a blood meal.
Adult females embed their eggs near the base of hair shafts, securing them with a cement-like secretion. Eggs hatch after 7–10 days, releasing nymphs that immediately begin feeding. Nymphs undergo three molts, each lasting 3–5 days, before reaching sexual maturity. The entire cycle from egg to adult can be completed in 2–3 weeks under optimal temperature and humidity.
Feeding involves several specialized adaptations:
- Piercing‑sucking mouthparts, called stylets, that penetrate the epidermis to reach capillary blood.
- Anticoagulant saliva containing enzymes such as apyrase, which prevents clotting and facilitates continuous blood flow.
- Sensory receptors on the tarsi that detect temperature and carbon‑dioxide gradients, guiding the insect toward suitable feeding sites.
During blood ingestion, the louse expands its abdomen, storing the meal in a distensible gut. Excess fluid is excreted as watery feces, which may cause irritation and secondary infection in the host. Reproductive output is high; a single female can lay 5–10 eggs per day, producing up to 300 eggs over her lifespan of about 30 days.
Transmission occurs primarily through direct head‑to‑head contact, although sharing combs, hats, or bedding can transfer eggs and mobile stages. Environmental survival is limited; without a host, lice die within 1–2 days, emphasizing the necessity of continuous access to blood for persistence.