**Lice** (order Psocodea, suborder Anoplura for sucking lice) are small, wingless, parasitic insects that live externally on warm-blooded hosts (humans, mammals, and birds). They are obligate parasites, meaning they must feed on blood or dermal secretions to survive. The primary conflict is the medical and social nuisance of infestation, including itching, skin irritation, and, in some cases, the transmission of pathogens like *Rickettsia* (Epidemic Typhus, carried by body lice). The three main types affecting humans are **Head Lice** (*Pediculus humanus capitis*), **Body Lice** (*P. humanus humanus*), and **Pubic Lice** (Crabs, *Pthirus pubis*).
Taxonomy and Classification
Lice belong to the order Psocodea. Sucking lice (Anoplura) are characterized by piercing-sucking mouthparts used to feed on blood. They undergo simple metamorphosis (egg, nymph, adult). They are highly host-specific, meaning human lice cannot live on or infest pets (dogs, cats) or vice versa. The eggs, called **nits**, are cemented firmly to the host’s hair shaft or clothing fibers.
Physical Description
Adult human lice are 1/16 to 1/8 inch long.
- **Appearance (Key ID):** Flat, tan or grayish body, with three pairs of strong legs equipped with claw-like tarsi (feet) designed for gripping hair shafts.
- **Nits:** Tiny, oval, whitish-yellow eggs, cemented near the base of the hair shaft (head lice) or along the seams of clothing (body lice).
- **Infestation Sign:** Intense **itching** (pruritus) on the scalp or body, small red bite marks, and the visible presence of nits stuck to the hair shaft.
- **Conflict:** Medical and social nuisance, itching, and potential disease vectoring (body lice).
Distribution and Habitat
Lice are found globally, often associated with crowded conditions or close personal contact. Head and Pubic Lice live directly on the host’s hair. Body Lice live primarily in the seams of clothing and move onto the skin only to feed, making them common where clothing is rarely washed or changed.
Behavior and Conflict
The conflict is medical, social, and vector-borne illness.
- **Transmission:** Lice are generally transmitted by direct contact (head-to-head contact, shared bedding, clothing, or combs). They cannot fly or jump.
- **Secondary Infection:** Constant scratching from the itching can lead to secondary bacterial skin infections.
- **Typhus (Body Lice):** Body lice are important vectors of serious diseases like typhus and trench fever, historically associated with mass displacement and poor sanitation.
Management and Prevention
Control focuses on chemical treatment and thorough hygiene.
- Use medicated shampoos containing pyrethrins, permethrin, or dimethicone.
- **Manual Removal:** Systematically comb out nits and lice using a fine-toothed lice comb (nit-picking).
- **Sanitation:** Wash all bedding, clothing, and towels in hot water (>130^\circ \text{F}). Items that cannot be washed should be sealed in plastic bags for two weeks.
- Treat the clothing and bedding with heat or laundering.
- Wash the body thoroughly and apply necessary topical creams.
Conservation and Research
Lice are managed as high-priority medical and veterinary pests. Research focuses on understanding insecticide resistance (which is becoming common), developing non-chemical treatments (e.g., heat or suffocating agents), and monitoring the species that act as disease vectors.