Why do female lice lay eggs in that way? - briefly
Female lice cement their eggs to hair shafts to keep them anchored and close to a food source for the emerging nymphs. This placement protects the eggs from being removed and enhances hatchling survival.
Why do female lice lay eggs in that way? - in detail
Female head‑lice (Pediculus humanus capitis) deposit their ova by securing each egg to a single hair shaft with a proteinaceous cement. This method results from several selective pressures.
The cement is secreted from the distal end of the abdomen as the ovipositor contacts the hair. It hardens within seconds, forming a robust attachment that resists mechanical disturbance, washing, and grooming. By anchoring the egg close to the host’s scalp, the embryo remains in a stable micro‑environment with constant temperature (≈ 33 °C) and humidity, conditions essential for embryonic development.
The positioning of the egg near the scalp also facilitates immediate hatching into a mobile nymph that can feed without needing to locate a new host. The nymph emerges from the operculum, which the female partially opens during laying, allowing the larva to emerge directly onto the hair shaft.
Key advantages of this oviposition strategy include:
- Protection from external forces: The cemented attachment prevents eggs from being dislodged by host movement or accidental contact.
- Micro‑climatic stability: Close proximity to the scalp maintains optimal thermal and moisture levels, reducing developmental delays.
- Reduced predation risk: Eggs hidden among dense hair are less visible to predators such as predatory mites.
- Efficient host transfer: Upon hatching, the nymph is already positioned to locate a feeding site, shortening the vulnerable period before the first blood meal.
The morphology of the egg reflects these functions. The shell is flattened, with a ventral operculum that opens only when the nymph is ready, and the dorsal surface bears ridges that increase surface area for cement adhesion. The cement itself contains glycoproteins that polymerize upon exposure to air, creating a strong, water‑resistant bond.
In summary, the combination of a specialized cement, precise placement on the hair shaft, and egg architecture maximizes survival rates by shielding the embryo, ensuring favorable developmental conditions, and enabling rapid post‑hatch colonization of the host.