The life cycle of Phthirus pubis, commonly known as the pubic louse or crab louse, consists of three main stages: egg (nit), nymph, and adult.
1. Egg (Nit) Stage: The life cycle begins when a female louse lays eggs, known as nits, on the hair shafts near the base of pubic hair. Nits are oval-shaped and are usually yellowish-white in color. They are firmly attached to the hair shafts and are difficult to remove. It takes around 6-10 days for the eggs to hatch.
2. Nymph Stage: Once the eggs hatch, nymphs emerge. Nymphs are smaller than adults and resemble miniature versions of them. They have six legs and are translucent or grayish-white in color. Nymphs require a blood meal to grow and develop. They go through three nymphal stages, known as instars, over a period of about 9-12 days. After each instar, the nymph molts and sheds its exoskeleton to grow into the next stage.
3. Adult Stage: After completing the third nymphal stage, the louse becomes an adult. Adult pubic lice are about 1-2 millimeters in length and have six legs. They are usually tan to grayish-white in color and have a crab-like appearance, which gives them their common name. Adult lice feed on blood and can survive for up to 30 days on a human host. They mate and reproduce, with females laying around 30-40 eggs during their lifespan.
The life cycle of Phthirus pubis is completed when the adult lice lay eggs, which then hatch into nymphs, and the cycle continues. The entire life cycle from egg to adult takes approximately 2-3 weeks.