How many years can lice live? - briefly
Lice survive only weeks, not years. An adult head louse lives about 30 days on a human host and up to roughly two weeks when detached.
How many years can lice live? - in detail
Lice are obligate ectoparasites; their entire life cycle depends on a living host. An adult head louse (Pediculus humanus capitis) typically survives 30 – 45 days on a human scalp. Body lice (Pediculus humanus corporis) show a similar adult longevity, ranging from 30 to 35 days when a host is available. Pubic lice (Pthirus pubis) live slightly longer, with adult lifespans reported up to 60 days under optimal conditions.
The life cycle consists of three stages:
- Egg (nit): incubation lasts 7‑10 days before hatching.
- Nymph: three instars develop over 9‑12 days; each molt requires a blood meal.
- Adult: after the final molt, the insect begins reproducing and lives for the period noted above.
Outside a host, lice cannot sustain themselves. They die within 24‑48 hours when deprived of blood, regardless of ambient temperature. Extreme cold or heat accelerates mortality; temperatures below 4 °C or above 45 °C reduce survival to a few hours.
Reproductive capacity influences population turnover. A single female lays 5‑8 eggs per day, producing up to 150 eggs in her lifetime. Rapid egg production compensates for the short adult lifespan, ensuring the species persists on the host.
Laboratory studies have extended adult survival to 60‑70 days by providing continuous blood access and controlled humidity (70‑80 %). These conditions are artificial; in natural settings, the maximum lifespan does not exceed two months.
Consequently, lice do not live for years. Their biological design limits existence to weeks, with the longest recorded adult survival just over two months under ideal laboratory conditions.