Lice: A Human Skin Parasite

The Parasite

The parasite is involved in a type of symbiotic relationship. A symbiotic relationship is one involving two organisms of a different species having a close relationship. Parasitism is the relationship between two organisms where one benefits from the relationship at the expense of the other. This is typically a closely associated relationship lasting for a long period of time. Lice is a human parasite, benefiting at the expense of its human host.

The Three Types of Lice

Lice, singularly known as louse, are found in every country and continent. There exist over 3,000 different species of these wingless insects. The most common include three types of lice that infect humans; including:

  • Head lice (pediculus humanus capitis)
  • Body lice (pediculus humanus corporis)
  • Pubic lice: Also known as crab lice (phthirus pubis)

Lice: Physical Characteristics

The physical characteristics of all three types of lice are very similar. All are approximately 2 millimeters in size, although the crab louse is the smallest and the head louse the largest. All lice are wingless, incapable of flying or jumping, and flat. Lice have six legs, three pairs, specifically located behind the head. These legs have sharp claws, used for the purpose of attachment to items and hair. Lice use these claws to pierce the skin, using specially designed mouthparts for sucking blood. While sucking blood, the lice secrete saliva, increasing the overall sensations of itching. Typically, lice are gray in color. This color may change to be considerable darker after a recent feeding.

Lice and Nits

The egg of a female louse is known as a nit. One healthy adult female louse is capable of producing 3 - 4 eggs per day. These nits are attached to the human hair through the use of specialized saliva. This saliva is produced by the louse and is responsible for the creation of bonding the nit to the hair. Nits are typically pale white in color when alive. If the nit appears a brown color, it is dead. Nits require approximately a one month maturation period, which is made up of three stages. All stages of maturation are associated with the need for blood as a food source.

Lice and Your Skin

Lice are specially designed for the infection of a specific host. Lice are limited in their capabilities of infection to specific areas of the body, as the need for hair is a necessity. Lice are dependent upon their host for survival, and because of this fact, lice have developed many characteristics to help maintain this close relationship. Lice feed on blood, which must be obtained through damage to the skin. Head lice are limited to the scalp. The scalp provides the necessary shelter, food, and reproductive environment required by the lice. Hair keeps the temperature consistent and warm, and is the location for nit placement. Food is found in the form of blood, and is readily available on the scalp. The itching created by this feeding is caused by the secretion of saliva by the lice.


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