What Is Head Lice?
Three important things you should know about lice are:
- Head lice are not a sign of bad hygiene; most often it’s just a case of touching heads with someone else who has lice.
- Head lice are not known to transmit any diseases.
- The lice eggs (nits) are what make head lice so hard to get rid of.
There are 3,000 species of lice, but there are only three species that affect humans. These are pubic lice, body lice and head lice.
Head lice feed exclusively on human blood. Lice are most common among children between 4 and 14 years of age. Girls are two to four times more likely to get lice than boys, but parents, caregivers, and anyone with close contact to children can get head lice. The Center for Disease and Control estimates that there are between 6 – 12 million cases of head lice each year in the United States. Those figures are based on the sale of lice shampoo/pediculicides.
Head lice are repelled by light; they prefer dark warm areas and are commonly found behind the ears and near the nape of the neck. Nits are also commonly found in those areas. Lice have six short legs with claws on the end of those legs that allow the lice to move quickly through hair. The claws are so specifically evolved that a change in the shape of the hair follicle will make for a difficult environment for the lice. For example the oval shape of the hair follicles of African Americans is the reason why head lice infestations among that demographic are so rare. Having said that there is a strain of head lice in Africa with claws that are adapted to the oval shape of the hair follicles of native Africans, and thus head lice is a problem among natives in Africa.
Because head lice are so well adapted for moving through hair they have a hard time moving through other mediums such as hats, or clothing, or flat surfaces, and the adult louse can only survive around 1-2 days away from its food source. When fighting lice, most of the focus should be on removing lice from the hair.
Feeding
Lice feed four to five times daily by piercing the skin with a stylet that comes out from the lice’s head when feeding. Lice inject saliva to thin the blood and prevent the blood from clotting during feeding. It is the lice saliva that causes itching. Lice may feed for a long period of time if left undisturbed.
Life Cycle of a Louse
Head Lice are well adapted to the human scalp, and spend their entire life cycle on the head. If head lice leave the safety of their environment they will quickly become weak and die. Lice are unable to survive for longer than about 48 hours off of the head.
The complete life cycle of a louse includes three stages: nit, nymph, and adult. It takes about one month for a nit to become an adult Louse that is capable of producing nits.
Nits:
Lice eggs are called nits. Nits
are attached close to the base of the hair shaft; they need the warmth
of the scalp for incubation. The nits are surrounded with a protein
glue except for the operculum, a cap through which the embryos
breathes. This glue cements the nits to the hair shaft and protects the
nits. This is why head lice are so hard to get rid of. Because of
this protective shell, the nit can withstand almost any chemical
treatment. Nits can also survive underwater for over 24 hours.
Nits are light brown and oval-shaped. When a nit hatches it leaves behind the empty nit sheath. The nit sheath remains on the hair shaft and are white in color. Nits are very small, about the size of this period (.) and people often misdiagnose lice for dandruff. Remember nits are glued to the hair shaft and won’t slide easily, but dandruff will. Nits usually take about 6 to 9 days to hatch.
Nymphs:
 The second stage of a Louse is the Nymph.
The nymph stage begins after the nit hatches and lasts between 8 to 12
days. During that time the nymph will molt out of its exoskeleton 3
times. Nymphs are about the same shape and color of lice, just smaller.
Adult:
 Adult lice are about the size of a sesame
seed and are grey in color. Their color changes to a rust color after
feeding. The adult female lays about three to four eggs each day.
During its lifespan of four weeks a female louse can lay 50–150 eggs
(nits).
|
