How do lice hatch from nits? - briefly
Within 7‑10 days at normal body temperature and sufficient humidity, the embryo inside the egg finishes development, the operculum splits, and the newly hatched nymph emerges ready to feed.
How do lice hatch from nits? - in detail
Lice eggs, commonly called nits, are firmly attached to hair shafts by a cement-like secretion produced by the female adult. The egg’s outer shell, or chorion, is composed of several layers that protect the developing embryo. Inside the chorion, a single embryo undergoes a series of developmental stages: cleavage, formation of a germ band, segmentation, and organogenesis. Throughout these stages, the embryo consumes yolk reserves stored in the egg’s interior.
Incubation temperature is the primary factor governing the duration of development. At typical human scalp temperatures (approximately 33–35 °C or 91–95 °F), embryogenesis completes in about 7–10 days. Cooler conditions extend the period, while higher temperatures accelerate it, but extreme heat can be lethal to the embryo.
When the embryo reaches the final larval stage, it produces an enzymatic secretion that weakens the inner layers of the chorion. Simultaneously, muscular contractions of the larva generate pressure against the weakened shell. This combination creates a small opening through which the newly hatched nymph emerges. The nymph is initially pale and immobile; it quickly expands its body, allowing hemolymph to circulate and cuticular hardening to occur. Within a few hours, the nymph begins feeding on blood, entering the first instar stage.
Key points of the hatching process:
- Attachment: Nits are glued to hair with a proteinaceous cement that resists removal.
- Development: Embryogenesis proceeds through defined morphological phases, sustained by yolk nutrients.
- Temperature dependence: Typical scalp heat yields a 7–10‑day incubation; deviations alter timing.
- Enzymatic weakening: The larva secretes chorion‑degrading enzymes near the end of development.
- Mechanical emergence: Muscular action forces the nymph through the compromised shell.
- Post‑hatch maturation: The nymph hardens, darkens, and initiates blood feeding within hours.
Understanding each stage clarifies why timely detection and treatment of infestations are essential; once hatching occurs, the nymph rapidly matures into a reproductive adult within approximately four days.