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Head lice are tiny creatures which live in human hair. If you have one, it is called a louse, but the plural (what you call lots of them) is lice. So, if you find one louse, it probably means you have head lice! And what are nits? Well, nits are the eggs that the lice lay in people's hair.
Head lice need human blood to grow, develop into adults and lay eggs. When on a human body, they usually live on the scalp, but can also live in eyebrows or eyelashes.
Head lice are quite small; adults are only a few millimetres long and the immature lice are even smaller. They are tan to grayish-white. Head lice cannot fly or hop like fleas, but they can crawl quickly through the hair at a rate of 20cm per minute.
An adult female head louse can lay 3-4 eggs per day and they usually live for 30 days. Eggs hatch within 7-10 days after being laid. Lice pass through three stages before becoming adults, which takes another 8-9 days. One pregnant adult female can produce enough offspring so that a lot of nits can be found in someone's hair within a month. A child that has a lot of nits has been infested for at least a month or more.
Nits are white when they are first laid and turn brownish before they hatch. They are glued to hair strands about one cm from the scalp. This glue is so strong that the nits cannot be as easily removed as dandruff and other hair debris. Even though some products claim to remove nits, there is no safe way to melt this glue. The nits have to be scraped off the hair.
Head lice must feed every few hours, but can survive off a human being for two days to a week depending on how warm it is. Lice die more quickly when temperatures are warm and humidity is low.