How do lice develop from nits? - briefly
Lice emerge from their eggs (nits) after roughly 7–10 days, at which point the newborn nymph looks like a miniature adult. The nymph then molts three times over the next 7–10 days before becoming a reproductive adult.
How do lice develop from nits? - in detail
Lice begin life as eggs attached to hair shafts with a glue‑like cement that hardens within hours. The egg, commonly called a nit, contains a fully formed embryo. Development proceeds inside the protective shell and requires stable temperature, typically 29‑32 °C, and adequate humidity; lower temperatures delay hatching, while extreme dryness can cause embryo mortality.
The incubation period lasts 7–10 days. During this time the embryo undergoes cellular differentiation, forming the head, thorax, abdomen, six legs, and sensory organs. A small operculum at one pole of the shell opens as the larva prepares to emerge. When the nymph breaks through, it measures about 1 mm and is pale translucent.
From hatching, the louse passes through three successive nymphal stages (instars). Each instar lasts 2–3 days and ends with a molt in which the exoskeleton is shed. The sequence is:
- First instar: active feeding on blood, rapid growth, development of darker pigmentation.
- Second instar: increased size, stronger mandibles, continued blood meals.
- Third instar: near‑adult morphology, readiness for final molt.
The final molt transforms the third‑instar nymph into a mature adult within 1–2 days. Adults measure 2–3 mm, are gray‑brown, and possess fully functional reproductive organs. Mating occurs shortly after emergence; females begin laying eggs after 1–2 days of adult life, depositing 5–8 nits per day.
The entire cycle—from egg to egg‑laying adult—typically spans 18–21 days under optimal conditions. Environmental factors such as temperature fluctuations, host grooming, and chemical treatments can extend or interrupt this timeline. Understanding each phase assists in timing interventions, as treatments targeting mobile stages (nymphs and adults) are ineffective against eggs until they hatch.