Biology Of Head Lice

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In my haste to get rid of head lice all I wanted to know about them was what they looked like, and how quickly, I could get rid of them.

Head louse, nits, eggs, nymphs or lice, call them what you like, this little pest has been an endless frustration to many families for years.

Information about the biology of head lice includes pictures of head louse, eggs and nits. Knowing how infestations start and where nits come from and how they evolved was the beginning of a journey for myself that got rid of head lice from my family life for-ever.


Head Lice are small (1–3 mm long), wingless little pests. With a head and abdomen that are distinctively obvious which is explained forth with.

Louse are grey in general, but their exact colour varies according to the environment in which they live. According to it's surroundings e.g hair colour etc

After feeding, the blood they consume cause their body to take on a reddish tinge.

The Head

Did you know that, adult head lice have?

  • One pair of antennae, each with five segments, protruding from it's head.
  • They also have one pair of eyes.
  • A mouth, adapted for piercing skin and sucking blood and when, not feeding the mouth is retracted back into the head.

The Legs

They have six legs that are short with a single claw and opposing thumb.

With their short legs and large claws, head louse are well adapted to clinging to the hair of their host, (that would be us, their human host)leaving them incapable of jumping, or even walking efficiently on flat surfaces.

The Abdomen

The abdomen has seven visible segments;

  • The first six segments each have a pair of spiracles through which they breathe.
  • The last segment contains the anus and (separately) the genitalia.


  • Viable eggs are little white/brown specks, that may look like dandruff. Unlike dandruff they are not easily removed.
  • Louse attach their eggs to strands of hair with a glue like substance approx 1cm or less from the scalp.
  • Eggs need warmth from the head of their human host to aid in the incubation process.
  • The incubation process lasts approx 7 days. When the egg hatches it begins the next stage of it's life as a nymph.
  • Being close to the scalp when they hatch is important, as they will need to feed almost immediately after hatching.

The further away from the scalp, the louse will dehydrate and die. Which is why they do not stray very far from the scalp as they will need to feed several times a day.

Differences between the "Egg and Nit".

The egg is found closer to the scalp, and the nit is found 1cm or more further down the hair strands.

Pictures magnify them depicting their differences. In reality, utilising your visual judgement is all that is required.

  • The Egg is recognized, by a cap on top of it's shell. Indicating, there is a viable egg present.
  • The Nit is recognized, by the absence of the cap, indicating the egg has hatched, leaving behind an empty shell.


A newly hatched nymph will moult three times before reaching the sexually-mature adult stage. After each moult, the discarded skeleton is later shed by the host and may be mistaken as a viable louse.

The only visible change between the nymphal stage and the adult, other than size, is the length of the abdomen, which increases with each moult.

The time required for head louse to complete their nymph development depends on feeding conditions. At minimum, eight to nine days is required for continuous access to a human host.

Aside from reproduction, nymph behavior is similar to the adult.

  • Feeding only on human blood.
  • They are unable to survive long away from a host.
  • Unable to fly or jump.

Head Lice Biology and Reproduction

Copulation is necessary for the female to produce fertile eggs, and can begin within the first 10 hours of adult life.

After 24 hours male and female will mate frequently, any time of day or night, with each attachment lasting more than one hour. Young males can successfully pair with older females, and vice versa.

Females lay about three to four eggs daily, while, during its lifespan of 35-40 days she will lay up to 50–150 eggs.

Mobile head louse populations contain members of up to five developmental stages

the egg, three nymph stages, and the adult louse.

All Living things procreate, these little pests are no different

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