Life Cycle of Pediculus Humanus

Pediculus humanus are better known as head lice. They are more common on children than adults, but are highly contagious only to other humans, not to pets. They cause the skin underneath hair to become intensely itchy. These parasites and their eggs, called nits, are treatable, and understanding the head lice life cycle is helpful in ridding yourself of these pests.

Eggs

• Head lice eggs attach very firmly to the base of a hair strand. They are generally white. They will not come off with a regular comb. Because they are so small, they need to be combed out with a nit comb, which is similar to a flea comb in that the teeth are incredibly close together. Eggs hatch about six to 12 days after they are laid. Empty egg shells will still remain stuck to the hair, and they will turn from white to yellow.

Juvenile

• After hatching, the nymphs resemble miniature versions of adult head lice. According to the University of California, newborn lice need a meal of human blood within minutes of hatching or they will die. They will also die of starvation if they are separated from a human host for more than 24 hours. Their saliva injects an anticoagulant to keep the blood from clotting. This is what causes the itchy sensation.

Moulting

• According to the Centers for Disease Control and Prevention, it only takes an average of seven to eight-and-one-half days for a newly-hatched nit to grow into a sexually mature adult. During this time, the nymph will go through three molts, where it sheds its old body's shell and emerges in a slightly larger body. In all of these stages, it must feed on human blood several times a day. Females will grow to be slightly bigger than males, but still, they only average between two to three millimeters long.

Adult

• In the adult stage, the lice either tries to find a breeding partner on its host or climbs down the ends of the hair shafts and drop off onto bedding, furniture, towels or clothing. They then look for another hairy human host to clamber up onto and breed. The fertile female louse then lays three to five eggs every day until she dies. From hatching to death, a louse lives for about 25 to 30 days.

Significance

• Because the head louse can reproduce so rapidly, it takes more than one medicinal treatment to get rid of an infestation. Medicated shampoos and lotions are available over the counter, and via a doctor's perscription. Bedding, clothing and furniture must be washed or spun in a hot dryer to kill any fallen lice. The affected person's head must be combed with a nit comb every day for at least two weeks to kill any newly hatched nymphs.