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Head Lice
Head lice are bloodsucking insects without wings. They are parasites
that feed on human blood. Head lice have ‘specialised’ in living on
human heads. Their specially shaped bodies and small oval heads ensure
that the lice can move easily through the hair. At 20 degrees Celsius,
head lice can move at around 30 cm per minute and the higher the
temperature, the faster they can move. Head lice have six legs, which
they use to attach themselves.
Generally speaking, head
lice and nits are most easily found behind the ears, along the
hairline and in the neck, since these areas are warm and dark. Head
lice can adapt their colour to the colour of the hair, which makes
them difficult to spot. The colour of the louse can vary from
sandy-coloured to nearly black but after feeding they become a
dark red. Head lice occur most frequently in children aged 5 to 12.
The eggs of the head louse are called `nits’. Eggs can survive for
around seven days. The life of a head louse is relatively short. Under
normal circumstances head lice live an average of 30 days. The life
cycle has three stages: egg, nymph and adult. In its lifetime, a
female louse will lay 100 to 300 eggs, an average of 6 per day. The
female louse attaches the nits to the hair with a kind of glue, no
more than 1 mm from the scalp. Nits stay firmly attached to the hair,
which means that the distance from the scalp increases as the hair
grows.
The position of the nits compared to the scalp is a way of measuring
the age of the nits, with a distance from the scalp of 1cm equating to
1 month old. Eggs are yellow-white to brown in colour and are about
the size of a pinhead. After a maximum of 10 days, a nymph
emerges from the nit and after a further 12 days or so, the nymph
becomes an adult louse, 3-4 mm in length.
The total development from nit to adult louse takes approximately 3
weeks, which means that in a relatively short period of time there can
be a complete re-infestation if nits are left untreated.
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