How does a louse grow? - briefly
Lice develop by incomplete metamorphosis: eggs hatch into nymphs that resemble tiny adults, and through successive molts they enlarge until reaching full adult size.
How does a louse grow? - in detail
A louse progresses through a defined series of developmental stages that are tightly linked to feeding on host blood. The life cycle begins with the deposition of an oval egg, or nit, firmly attached to hair shafts by a cementing substance. The egg measures roughly 0.8 mm in length and requires 6–10 days of incubation, depending on temperature and humidity. During this period the embryo undergoes embryogenesis, forming the basic body plan, mouthparts, and sensory structures.
Upon hatching, the immature insect emerges as a first‑instar nymph. This stage is pale, wingless, and measures about 1 mm. The nymph immediately begins to feed, ingesting blood to fuel its growth. Each successive molt enlarges the organism and adds a new set of sclerotized cuticle layers. The molting sequence includes:
- First instar – lasts 2–3 days; size increases to ~1.5 mm.
- Second instar – duration 2–3 days; size ~2 mm.
- Third instar – lasts 3–4 days; size ~2.5 mm.
- Fourth instar – lasts 3–4 days; size ~3 mm.
After the fourth molt the louse reaches the adult stage. Adults measure 2.5–4 mm, exhibit full pigmentation, and possess functional reproductive organs. Females lay eggs continuously, typically 5–10 per day, maintaining the population cycle.
Growth rate is temperature‑dependent: optimal development occurs at 30 °C (86 °F) with relative humidity above 70 %. Lower temperatures extend each stage, while extreme heat or desiccation can halt development or increase mortality. Nutrient intake from blood directly influences molting frequency; insufficient feeding delays progression and may trigger premature death.
In summary, a louse’s growth comprises embryonic development within a nit, four nymphal molts fueled by blood meals, and maturation into a reproducing adult. Environmental conditions and host availability govern the speed and success of each phase.