BiologyLice Life Cycle

Lice Life Cycle

Lice are tiny, wingless parasitic insects. They live on the skin of various animals, including humans. There are different types of lice, each adapted to a specific host species.

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    Types of Lice

    The three main types of lice:

    1. Head Lice (Pediculus humanus capitis): These are the most common type of lice found in humans. They live on the scalp, feeding on human blood, and are particularly prevalent among school-aged children. Head lice are spread mainly through direct head-to-head contact.
    2. Body Lice (Pediculus humanus corporis): These lice live in clothing and bedding and move to the human body to feed. Body lice infestations are often associated with poor hygiene and living conditions and can spread diseases.
    3. Pubic Lice (Pthirus pubis): Commonly known as “crabs,” these lice infest the pubic hair and sometimes other coarse body hair. They are usually spread through sexual contact.

    Lice Life Cycle

    What is the Lice Life Cycle?

    Lice have a short lifespan but reproduce quickly. Female lice lay eggs (nits) that attach firmly to hair strands near the skin. These nits hatch into nymphs, which mature into adult lice.

    Nit (Egg):

    Head lice eggs, commonly known as nits, are tiny, measuring between 0.8 to 0.3 millimetres in size, and have an oval or teardrop shape. Their colour can vary, including white, yellow, tan, or brown, making them difficult to spot.

    When alive, the eggs appear darker and can be popped between fingernails. Once hatched, they turn pale or almost translucent, and the sides appear shrivelled if the eggs are dead due to lice treatment.

    A female adult louse attaches each egg to an individual hair shaft, approximately 6 mm from the scalp, to ensure the right temperature for hatching. The eggs are held in place with a strong, cement-like substance, making them resistant to washing, chemicals, and hairstyling.

    The incubation period for nits is 6–9 days, requiring the warmth of the scalp. If they are dislodged from the hair, they will unlikely survive until hatching.


    Nymphs, or baby lice, resemble miniature adult lice and are about the size of a pinhead, measuring 1.1–1.3 mm. They move to the scalp to feed on blood daily. Nymphs go through three molting stages, shedding their skin before they become adults. This entire development process spans up to 10 days:

    1. The first molt happens 2 days after hatching.
    2. The second molt takes place 5 days after hatching.
    3. The third molt occurs 10 days after hatching.

    Adult Louse

    When they reach the adult stage after the third molt, lice are darker, with colours ranging from tan to greyish-white to brown, and are approximately the size of a sesame seed, or 2–3 mm. Typically, female lice are larger than males.

    Adult lice start mating, and females can lay their first egg within 1–2 days after mating. They can lay up to eight nits daily and continue to produce eggs throughout their lifespan. A mated female louse needs to mate only once to keep producing eggs continuously, as they can store sperm within their body.

    Adult lice need to feed on blood multiple times daily and can live up to 30 days on a human head. However, they can only survive about 2 days away from the host, requiring constant feeding and an optimal temperature.

    Life Cycle of Lice on Humans and Other Objects

    Nymphs, the newly hatched lice, immediately require food. They use their claws to crawl from hair strands to the scalp, where young adult and mature lice feed on the host’s blood several times daily.

    An adult louse can survive up to 30 days on a human, provided a consistent food source. During this time, female lice can lay up to six eggs daily, rapidly increasing the lice population.

    It’s important to note that lice cannot spread from humans to pets. Even pets with hair, like dogs and cats, cannot transmit lice.

    Regarding the lifespan of lice on inanimate objects or without food, adult lice cannot survive longer than about 24 hours on non-human surfaces such as carpets, hardwood floors, clothing, furniture, sports helmets, headphones, or hair accessories. In cases where lice are found in the home, isolating and washing potentially affected items and areas within at least 72 hours is recommended.

    Nits, the lice eggs, also require a human host to survive. They need the warmth of the scalp for incubation and, upon hatching, nourishment from human blood. Nits removed from a hair shaft will likely die before they hatch.

    Signs and Symptoms of Head Lice Problem

    People with head lice often exhibit no symptoms. However, several indicators may suggest the presence of head lice:

    1. Frequent itching of the head or scalp: This is usually caused by an allergic reaction to lice bites.
    2. Redness or inflammation on the scalp or near the hairline: The scalp may become irritated and inflamed due to the lice feeding and moving around.
    3. Tiny red bumps or sores from scratching: Persistent scratching due to the itchiness can lead to small red bumps or sores on the scalp.

    What should be done in case of lice infestation?

    Lice infestations are characterised by itching, an allergic reaction to the lice bites. The presence of lice can be confirmed by visually spotting live lice or nits close to the scalp. Treatment typically involves using medicated shampoos or lotions specifically designed to kill lice.

    Additionally, combing wet hair with a fine-toothed lice comb can help remove lice and nits. It’s also important to wash clothing and bedding in hot water to eradicate lice that may have transferred to these items.

    Lice Life Cycle – Interesting Facts

    The life cycle of lice is fascinating and includes several stages, each with its unique characteristics:

    Egg (Nit) Stage:

    • Resilience: Lice eggs are incredibly resilient. The female louse secretes a glue-like substance that firmly attaches each egg to the hair shaft, making them resistant to regular shampooing, brushing, and even some chemical treatments.
    • Temperature Sensitivity: Nits need the warmth of the human scalp to hatch. They are typically laid about 6 millimeters from the scalp to maintain the ideal temperature for development.

    Nymph Stage:

    • Rapid Growth: After hatching, the nymph goes through three stages of molting. It looks like a smaller version of an adult louse and overgrows, shedding its skin as it matures.
    • Feeding: Nymphs start feeding on human blood almost immediately after hatching, essential for their growth.

    Adult Stage:

    • Short Lifespan but Rapid Reproduction: An adult louse lives for about 30 days on a human host. During this time, a female louse can lay up to six eggs per day, leading to a fast population increase if not treated.
    • Dependency on Human Blood: Lice feed on human blood several times daily. Without these blood meals, they cannot survive for more than a day or two of the host.

    Survival Tactics:

    • Clinging Ability: Lice have strong claws at the end of each of their six legs, allowing them to stick tightly to human hair, making them difficult to remove.
    • Colour Adaptation: Lice can adapt their colour to their environment, often matching the hair colour of their host, which helps them evade detection.

    Transmission and Limitations:

    • Human-to-Human Transmission: Lice are primarily spread through direct head-to-head contact. They cannot jump or fly but crawl efficiently from one head to another.
    • Ineffectiveness on Pets: Human head lice cannot live on pets; they are specifically adapted to feed on human blood.

    Environmental Resilience:

    • Survival Away from Host: While adult lice can only survive about 24 hours away from a human host, nits can live for a more extended period off the head, but they need the warmth of the scalp to hatch.

    Understanding these aspects of the lice life cycle is crucial in effectively managing and treating infestations.

    FAQ son Lice Life Cycle

    How long is a lice life cycle?

    A louse goes from egg to adult in about 2-3 weeks. Eggs (nits) hatch in 7-10 days, nymphs mature in another 7-10 days, and adults live for around 30 days. So, the life cycle of lice takes about a month under ideal conditions

    How long until the lice is entirely gone?

    Even with treatment, getting rid of lice completely can take longer than the life cycle of lice. Most medications only kill live lice, not eggs. So, you may need repeated treatments 7-10 days apart and regular checks for 2-3 weeks to ensure no new lice hatch.

    What kills head lice fast?

    There's no magic bullet for instant lice annihilation. Over-the-counter (OTC) lice treatments like permethrin or pyrethrin shampoos can be effective, but they must be applied correctly and followed up with thorough combing to remove nits. Prescription medications offer another option. Consider a doctor or pharmacist for guidance before using any lice treatment.

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