How can one tell if a louse is alive? - briefly
Visible locomotion or a reflexive twitch confirms the parasite is alive. Applying a light tactile stimulus causes it to crawl or vibrate.
How can one tell if a louse is alive? - in detail
Determining whether a louse is living requires observation of specific physiological and behavioral indicators.
Movement is the most immediate sign. A living specimen will walk, crawl, or exhibit rapid, jerky motions when disturbed. Lack of any motion, even after gentle stimulation, usually indicates death.
Response to tactile or thermal stimuli provides further confirmation. Light touch with a fine brush or a brief puff of warm air should provoke an immediate reaction, such as a change in direction or a brief pause. Absence of response suggests inactivity beyond normal rest periods.
Visible characteristics under magnification reveal additional clues. Living lice maintain a translucent, slightly glossy exoskeleton; a dull, opaque appearance often correlates with desiccation. The abdomen of a viable louse contains clear hemolymph; a darkened or collapsed abdomen signals necrosis. Respiratory movements can be seen as faint rhythmic expansions of the thoracic spiracles.
Feeding behavior distinguishes living individuals from dead ones. Active lice attach to hair shafts and insert their mouthparts into the scalp, creating a small, dark spot where blood is ingested. Observation of freshly engorged abdomens or the presence of blood droplets near the mouthparts confirms recent feeding activity.
Practical assessment steps:
- Use a fine-toothed comb on a small section of hair, collecting any attached insects on a white paper background.
- Examine each specimen under a handheld magnifier (10‑30×).
- Observe for spontaneous movement or reaction to a gentle probe.
- Check for translucency, abdominal fullness, and spiracle activity.
- Note any fresh blood residue near the mouthparts.
These criteria together allow reliable identification of living lice, facilitating appropriate treatment decisions.