How are human lice born? - briefly
Human lice reproduce by the female depositing 1–10 eggs (nits) on hair shafts each day, which hatch after 7–10 days; the emerging nymphs undergo three molts before reaching adulthood. The entire cycle from egg to adult lasts approximately 2–3 weeks under optimal conditions.
How are human lice born? - in detail
Human lice reproduce through a strictly oviparous cycle. Adult females lay eggs, called nits, on the hair shaft close to the scalp where temperature is optimal for development. Each female can produce 5‑7 eggs per day, accumulating up to 150 eggs over her lifespan of about 30 days.
The egg‑laying process involves the female using her ovipositor to cement each nit to the hair with a strong, protein‑rich glue. The glue hardens within minutes, securing the egg against mechanical removal. Nits are oval, 0.8 mm long, and have a characteristic operculum (cap) at one pole.
Embryogenesis proceeds through three stages:
- Cleavage and gastrulation (first 2‑3 days) – rapid cell division forms the embryo’s basic tissue layers.
- Organogenesis (days 4‑7) – development of mouthparts, legs, and sensory organs.
- Maturation (days 8‑10) – formation of the exoskeleton and preparation for hatching.
After approximately 8‑10 days at 30‑32 °C, the nymph emerges by pushing the operculum open. The newly hatched nymph is pale, wingless, and measures about 1 mm. It undergoes three successive molts (instars) at intervals of 2‑3 days, each molt increasing size and pigmentation. The final molt yields the adult, capable of reproduction within 5‑7 days of emergence.
Key biological parameters:
- Incubation period: 8–10 days, temperature‑dependent.
- Hatching success: 90 % under optimal conditions; drops sharply if humidity falls below 40 % or exceeds 80 %.
- Developmental time to adulthood: 14–18 days total from egg to fertile adult.
- Reproductive output: up to 150 eggs per female, ensuring rapid population expansion.
The entire cycle—from egg deposition to the next generation of egg‑laying adults—can be completed in less than a month, explaining the swift infestation potential in human hosts.