Pubic louse (also known as 'crabs')

Scientific Name: Pthirus pubis

Order & Family: Order Psocodea (formerly Anoplura), Family Pthiridae

Size: 1.1 mm to 1.8 mm (roughly the size of a pinhead)

Pubic louse (also known as 'crabs')

Natural Habitat

Exclusively on humans, primarily inhabiting coarse bodily hair such as pubic hair, but occasionally found in armpits, chest hair, or eyelashes.

Diet & Feeding

Obligate hematophage; it feeds exclusively on human blood several times a day.

Behavior Patterns

Slow-moving and sedentary; they use specialized claws to grasp hair shafts and remain close to the skin. They cannot jump or fly. The life cycle consists of the egg (nit), three nymphal stages, and the adult, spanning about 25–30 days.

Risks & Benefits

Risks include intense itching (pruritus) due to an allergic reaction to their saliva, and potential secondary bacterial skin infections from scratching. They are typically transmitted through close physical or sexual contact. Benefit: None to humans; they are strictly parasitic.

Identified on: 3/17/2026