The Louse Finds a New Home
The perpetuation of the life cycle of human lice begins the moment one louse is transferred from one person to another. Contrary to popular notions, human lice cannot jump or fly from one person to another. Only through physical or sexual contact with an infested individual or by sharing certain personal items that a lice temporarily inhabit, such as caps, hats, hairbrushes, clothing and bedding, can lice be spread. Human lice come in three species--head lice (Pediculus capitis), body lice (Pediculus humanus) and pubic lice, also know as crabs (Pthirus pubis). But the way in which they reproduce and their respective life cycles are essentially the same.
The Life of the Head, Pubic and Body Louse
Infestation begins when a sole impregnated female louse wanders onto a new human host and makes a habitat in the hair of the head or genital region or in the person's clothing. Head and pubic lice both lay their eggs close to the base of the hair shaft. Eggs are attached to the hair with a firm gluey substance that makes them difficult to remove. Head lice eggs (nits) hatch into "nymph" lice in about 5 to 10 days and develop into mature adults in 18 to 20 days, after which they breed, creating more impregnated female lice. Head lice live for about a month. Pubic lice, which are darker in color than head lice and have a unique "crab" shape, have a variable lifespan. In her three- to four-week lifecycle, one female louse lays about 30 eggs. Unlike head lice, which tend to wander, crabs stick close to where their eggs were laid for their entire lives. Body lice are physically similar to head lice. However, they lay eggs in the fibers of a person's clothing. A female louse can deposit around 9 to 10 eggs daily, for a total of 270 to 300 eggs during her lifetime. Human body heat "incubates" the eggs, but temperatures over 100 or below 75 degrees F prevent eggs from hatching. Body lice develop in about three to five weeks.
Breaking the Reproductive Cycle
Just like it only takes one impregnated female to infest a human host, all it takes is one successful mating of adult lice to create an infestation. Removing human lice infestations means breaking the louse's life cycle. Topical louse control medications with pesticide properties can be purchased over the counter or prescribed by a physician. But because head and pubic lice can survive for up to 24 hours without a human host--and body lice for up to 48 hours--treatment of the environment is also necessary. Clothing, towels and linens should be washed in hot, soapy water and dried on high heat for 20 to 30 minutes, and carpets, rugs and other soft furnishings thoroughly vacuumed.