Understanding ‘little white nits’

2013-07-11 00:00

I WONDER how many parents have been asked to take their children out of school until they are free of lice. This happened to us when the children were at primary school.

When we investigated further, we were told that our child had “little white nits” in her hair and that suitable treatment was necessary. Although we could find no trace of lice, we didn’t argue but merely got the necessary insecticidal shampoo and sent the child back to school. As I’m sure our experience is not unique, let’s chat about lice.

Lice are a diverse, but relatively poorly known group of insects called Phthiraptera, a name most people find tongue-twisting. All lice are wingless parasites of birds and mammals.

While we humans are troubled by two species, the pubic louse and the head and body louse, we will confine our discussion to the latter. The head and body louse, Pediculus humanus, has two subspecies — one that lives in the hair on our heads and one that lives elsewhere on our bodies, and is found mainly in our clothing.

One of the books I have consulted suggests that these two forms of the same species actually differentiated, following the invention of clothing some 100 000 years ago. Be that as it may, both subspecies have a similar and fairly simple life cycle.

Adult head lice mate and lay eggs, usually by cementing them to the bases of hairs. The eggs take about eight days to hatch into tiny nymphs. The nymphs feed on skin and blood, and moult twice before reaching adulthood; the juvenile stages lasting some 16 to 19 days.

Sexual maturity is reached in about two days and so the entire life cycle can be repeated in a period of about a month. Quite obviously, regular bathing and general cleanliness are usually sufficient to discourage lice from becoming a problem.

Unfortunately, it is relatively easy to pick up lice from people who are infested; all you need to do is make physical contact with them. But the fact that your child has a few nits is not necessarily evidence of having a breeding colony of lice. Fresh eggs are laid close to the scalp and quickly become grey in colour as the nymphs develop within them.

When a nymph hatches, the egg shell is left behind, which is then a whitish colour. So by the time one encounters white nits, the nymphs have long hatched and may well have been washed away by normal grooming.

So the presence of white nits merely says that an adult louse was there and that it laid an egg which hatched. It does not necessarily mean that there are living lice still present.

These insects cause great irritation and would cause the person concerned to take the necessary steps to rid him or herself of the problem. Chemists stock the necessary remedies.

Most people are amazed when they hear how many species of lice there are. However, if you consider that lice are highly specialised parasites that have evolved together with their specific hosts over millions of years, you will realise that virtually every species of mammal or bird has their own unique lice.

Those of us who are concerned about retaining our bio-diversity must accept that healthy populations of lice are just as important as healthy populations of their host animals.

Let’s briefly consider the current plight of our rhinos. The truth of the matter is that should we lose the war against poaching and rhinos become extinct — so do all the species of parasitic animals that have evolved together with rhinos. Rhinos are hosts of a number of unique parasites, both external and internal, and so we would lose a whole suite of wildlife if we lost rhinos.

Makes you think — doesn’t it?

• Dr Jason Londt is a natural scientist with a special interest in entomology. He welcomes queries and comments, which can be sent to him at jasonlondt@telkomsa.net. Please do not send large attachments.

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