What Is A Louse (Phthiraptera)?
What is a louse? A louse, also known as Phthiraptera, is a very small, wingless, parasitic insect. There are almost 5,000 varieties of lice living on almost every species of bird and mammal in the world.
Three types of lice live on humans: head and body lice are related subspecies, and pubic lice is a third. Lice have evolved so specifically over the entire course of human existence that these three types of lice can each only survive on the human scalp, body, and pubic area, respectively.
Life cycle of the louse
All lice have a three-part life cycle from egg, to nymph, to adult. The length of each stage varies slightly from one species to the next.
- Egg — Most species of female lice cement their eggs—called nits—to the base of feathers or hair follicles. (The human body louse lays eggs in clothing that is warm against the skin of the host.) Lice nits may take anywhere from six days to two weeks to hatch. Human head lice, for example, take about seven days to hatch.
- Nymph — The lice nymph that emerges from a mature egg looks almost identical to a grown louse, except it is smaller and generally lighter in color. A nymph louse grows through three stages of molting before reaching adult-size. The human head louse is full grown in about nine to 12 days.
- Adult — Safe and well-fed, the adult louse will live for about 30 days. The human head louse, for example, feeds several times per day.
A female, human head louse can lay as many as eight nits per day during adulthood, which means the population of a head lice community grows exponentially.
The degree of host restriction in lice is remarkable. That nearly 5,000 subspecies and varieties of lice have evolved over the ages speaks to how specified these insects have become. Almost any individual louse is only able to survive on a particular species of mammal or bird, and some can only survive on a specific part of a certain animal.
Human head, body, and pubic lice are one set of examples, but many warm-blooded hosts have a similarly specialized collection of lice subspecies. Some mammals, for example, experience up to 15 different types of louse that have evolved to survive on a specific part of the animal.
This host-specificity is probably the result of the louse’s close dependence on its host. Most lice, with the singular exception of the human body louse, spend their entire lives on their hosts. They cannot survive long without the warmth and nourishment of the host, so spreading to other organisms is not common.
Diversity and evolution of lice
Over time, each subspecies of lice—bound to a single host species—likely evolved unique physical features to survive on its specific bird or mammal … reinforcing the host restriction of the louse.
Most researchers believe, for example, that this is why the human head lice common in Europe, North America, and Australia is so rarely found in Black hair: The claws of that subspecies are not as effective on the more oval-shape of Black hair follicles.
Today, the several thousand types of lice can be categorized into two groups: chewing and sucking lice.
- Chewing lice, also sometimes called “biting lice,” (Ischnocera and Amblycera) live on both birds and mammals. This louse is a scavenger, feeding on dead skin; pieces of hair, fur, or feathers; and other debris on the host.
- Biting lice (Anoplura) only live on mammals. This louse has special mouth adaptations to pierce the host’s skin, so it can feed on blood and other bodily secretions.
Chewing lice are often slightly larger than biting lice, but they look very much the same—especially to the naked eye. The main physical difference is the mouth parts that are adapted to either chewing or biting.
The three subspecies of lice that can live on humans have likely been evolving with us for our entire natural history. There are no fossil records, but researchers have used DNA to trace the history of different species of lice.
Lice that are common in the West today likely descended from the group designated “clad B.” There is a noticeable split of one species into two (into what is now human head and body lice) roughly 100,000 years ago—coinciding with the time that Homosapiens may have started developing clothing.
Lice continue to evolve
The louse isn’t done. Just as they probably evolved when humans began wearing clothing, they are evolving still.
Decades ago, two medications were developed to help kill and remove head lice: permethrin and pyrethrin. Today, these are still the most common active ingredients in over-the-counter lice shampoos and treatments, but they are almost completely ineffective.
Because 98% of the head lice in the West today are what experts call “super lice.” They have developed a resistance to permethrin and pyrethrin. In order to make sure that you and your children aren’t the next generation of head lice hosts, you need a better head lice treatment option.
The good news is that several all-natural solutions are still very effective at treating head lice, and the Novokid system makes them extremely easy to use. See how a 10 minute, dry vapor treatment can help prevent and treat head lice.