Head Lice, heir Eggs, Their Life Cycle

The Head Louse

The head louse is a small wingless insect, which body is flattened. Its color is white but once soaked with blood, it becomes red or black. It measures 2 to 3 mm. Wingless, it does not fly nor does it jump but it moves quickly (speed of 23 cm per minute under natural conditions) between the hair to which it clings tightly with 3 pairs of short legs. Its abdomen is wider than the rest of the body.

The head louse breathes through holes that can close themselves and become impermeable to water. These openings also have a function of excretion. Its head has short antennae and highly specialized mouthparts that allow the head louse to perform piercing and sucking actions. He is feeding exclusively on the blood of its host, who it bites 2 to 4 times per day for meals that last about 30 minutes. It can live on the scalp for over a month (30 to 40 days).

Far away from his host, the head louse rarely survives more than 36 hours, it dies of starvation or dehydration. It must indeed be regularly fed with blood, and the weather and moisture conditions necessary to its survival are quite strict: temperature between 28 and 32°C with 70% to 80% humidity. The head louse is an external parasite of humans, which means that it absolutely must be on a human in order to survive. We know of no head lice predators.

Head Lice Eggs
 
The eggs of head lice are called nits and have the appearance of grain with a caramel color when laid, and they become more or less white when they are empty. Nits are very hard to spot as they measure approximately 0.8 mm and are glued to the hair by a secretion of the female louse. This secretion (cementum) coats the base of the nit and the hair which hold together firmly.

The female lays its nits at the root of the hair very close to the scalp (less than 1 mm) where the incubation is easier thanks to the heat and humidity. After hatching, the empty shell of the nit can remains on the hair for several months. Whitish, it gradually moves away from the root as the hair grows. Empty nits can easily be taken for dandruff but unlike those, they are resistant to washing and brushing hair.

The life cycle of head lice

Lice reproduce very quickly. The male is a tireless lover who can fertilize 18 females in a row without having a rest. The females mate several times during their adult life that can vary from ten to forty days. They lay from 4 to 10 eggs or nits daily for about 3 to 5 weeks, which means a total of 100 to 300 eggs or nits.

The nits hatch occurs after 7 days, giving birth to a larva. The latter resembles the adult but of course is smaller, measuring about 1 mm. The adult stage is reached after approximately 10 days after 3 successive molts. Thus from the laying of the egg to the emergence of the adult there are 17 days, and the adult will live for 30 to 40 days.

Since the 1970s, there has been a global increase in the number of cases of pediculosis. It is considered by some authors as the most common contagious disease in schools, after respiratory infections. Indeed it affects mainly children, and particularly children from 5 to 11 years. Head lice are present all year with peak periods (summer and autumn).