Head lice (Pediculus humanus capitis) are tiny, wingless insects that live exclusively on the human scalp and feed on human blood. These obligate parasites are a common concern, especially among school-age children, due to their rapid reproductive cycle. Understanding their reproductive needs is the first step in managing an infestation.
Required: Sexual Reproduction in Head Lice
Head lice require sexual reproduction between a male and a female to produce viable offspring. The female louse must mate with a male to ensure her eggs are fertilized before she can begin laying them. A single, unfertilized female cannot start an infestation because the eggs she lays would not be fertile.
The species does not reproduce through parthenogenesis, which is a form of asexual reproduction where a female produces offspring without fertilization. After copulation, the female louse is able to store the sperm. This stored sperm allows her to continuously lay fertile eggs throughout her adult lifespan, which typically lasts about 30 days.
Identifying Male and Female Lice
Successful reproduction depends on the presence of both sexes. Head lice exhibit sexual dimorphism, meaning there are noticeable physical differences between the sexes. The female louse is generally larger than the male.
Adult lice are small, about the size of a sesame seed, and are tan to grayish-white in color. Both sexes have six legs with specialized claws for grasping hair. The male’s posterior is often more rounded and darker due to the presence of reproductive organs. Recognizing these adult forms confirms a breeding population is present during an infestation check.
The Mechanics of Laying Nits
Following mating and fertilization, the female begins the process of laying eggs, which are commonly called nits. A female louse can lay between six and ten eggs per day for the duration of her adult life. These oval-shaped eggs are approximately 0.8 millimeters long and are firmly attached to the hair shaft.
The female secretes a strong, cement-like substance from her reproductive organ, which quickly hardens into a sheath that secures the nit to the hair. This adhesive bond makes nits difficult to remove and helps differentiate them from simple dandruff or other hair debris. The eggs are typically laid within a quarter-inch of the scalp, as they require the warmth of the host’s head to incubate. Nits take about six to nine days to hatch into nymphs, after which the empty eggshell remains firmly attached to the hair.