How do lice grow? - briefly
Lice progress through three nymphal instars, each requiring a blood meal before molting to the next stage, and then become reproductive adults. Under suitable temperature and humidity, the complete cycle from egg to adult lasts roughly 7–10 days.
How do lice grow? - in detail
Lice develop through a direct, incomplete metamorphosis that consists of three distinct stages: egg, nymph, and adult.
Female lice deposit oval, translucent eggs—commonly called nits—onto hair shafts close to the scalp. Each egg measures about 0.8 mm in length and is secured with a cement-like substance that hardens within minutes. Incubation requires a stable temperature of roughly 30 °C (86 °F) and a relative humidity of 70–80 %. Under optimal conditions, embryogenesis completes in 7–10 days, after which the nymph emerges by breaking the operculum at the egg’s pole.
The newly hatched nymph resembles a miniature adult but lacks fully developed reproductive organs. It undergoes three successive molts, each lasting approximately 2–3 days. Molting is triggered by feeding on blood; the ingestion of a sufficient volume of host plasma initiates hormonal changes that drive ecdysis. After the third molt, the insect attains the adult form, measuring 2–4 mm in length and possessing functional wings of reduced size (wingless morphology). Adult lice become capable of reproduction within 24 hours of reaching maturity.
Female adults lay 5–10 eggs per day, embedding them near the scalp where temperature and moisture remain constant. The reproductive cycle repeats continuously, allowing a population to double every 4–6 days if unchecked. Longevity of an adult ranges from 30 to 40 days, after which death typically results from starvation, host grooming, or environmental extremes. Temperature below 20 °C (68 °F) slows development, extending each stage by several days, while temperatures above 35 °C (95 °F) increase mortality.
Key factors influencing growth include:
- Host blood availability: Frequent feeding accelerates molting and egg production.
- Ambient humidity: Levels below 50 % cause egg desiccation, reducing hatch rates.
- Temperature stability: Fluctuations disrupt hormonal regulation of development.
Understanding each phase of the lice life cycle enables targeted control measures that interrupt egg viability, nymph maturation, or adult reproduction.