How do lice react to water? - briefly
Lice drown when fully submerged because they lack a respiratory system that functions in liquid. Brief contact may immobilize them, but sustained exposure results in rapid death.
How do lice react to water? - in detail
Lice are obligate ectoparasites that depend on a host’s body temperature and blood supply. Their physiology is adapted to a dry, warm environment; immersion in water triggers several immediate and longer‑term effects.
When a head louse contacts water, the exoskeleton absorbs moisture, causing the cuticle to swell. This swelling interferes with the articulation of the legs and claws, leading to loss of grip on hair shafts. The insect’s respiratory system, which relies on a network of tracheae open to the external atmosphere, becomes flooded. Oxygen exchange ceases, and the louse quickly becomes immobilized.
The nervous system reacts to the sudden change in osmotic pressure. Sensory receptors on the antennae detect the presence of liquid, prompting a reflexive attempt to climb upward. If the water level exceeds the insect’s body length, the upward movement is insufficient, and the louse sinks. In laboratory observations, most specimens drown within 30 seconds of submersion.
Survival after brief exposure depends on several factors:
- Duration of contact: Less than 5 seconds generally allows recovery; the cuticle re‑desiccates and normal locomotion resumes.
- Water temperature: Cold water slows metabolism, extending the time before immobilization; warm water accelerates cuticle swelling.
- Presence of surfactants: Soaps and shampoos reduce surface tension, facilitating entry of water into the tracheal openings and increasing mortality.
- Stage of development: Nymphs, with thinner cuticles, succumb faster than adult lice.
If a louse is only wetted, not fully submerged, it can retain viability. The insect will groom its body, using its claws to remove excess fluid, and resume feeding within minutes. However, repeated wetting events weaken the cuticle, making the parasite more vulnerable to mechanical removal and chemical treatment.
In summary, direct immersion leads to rapid loss of grip, respiratory blockage, and death within seconds, while brief surface wetting causes temporary immobilization followed by recovery, with outcomes modulated by exposure time, temperature, chemical agents, and life stage.