Why are there lice but no nits? - briefly
Adult head lice are observable, whereas their eggs remain glued to hair shafts and blend with debris, making them hard to detect as distinct organisms. Consequently, people often notice lice without recognizing the attached nits.
Why are there lice but no nits? - in detail
Lice survive because they feed exclusively on blood or skin debris, a resource constantly supplied by their hosts. Their life cycle includes three stages: egg (commonly called a nit), nymph, and adult. Eggs are laid firmly attached to hair shafts using a cement produced by the female; this cement hardens within hours, making the eggs resistant to removal and environmental stress. The eggs hatch after about 7–10 days, releasing nymphs that mature into reproductive adults within another 7–10 days.
The apparent absence of eggs in an infestation can be explained by several factors:
- Timing of inspection – Eggs hatch quickly; if a host is examined several days after a primary infestation, most eggs may already have emerged as nymphs.
- Effective treatment – Pediculicidal products often contain ovicidal agents that destroy eggs shortly after application, leaving only live insects visible.
- Host grooming – Regular combing or shampooing can detach or crush eggs, reducing their number on the scalp.
- Egg placement – Females preferentially deposit eggs near the scalp where temperature is optimal; these locations may be less accessible during visual checks, leading observers to miss them.
Understanding the biology of the parasite clarifies why adult insects may be observed while the egg stage seems absent. The rapid development cycle, combined with effective removal methods and inspection timing, creates a situation where lice are present but their eggs are not readily detected.