Pubic Louse (commonly known as "Crabs")

Scientific Name: Pthirus pubis

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

Size: Very small, typically 1.1–1.8 mm in length (slightly smaller than a sesame seed).

Pubic Louse (commonly known as "Crabs")

Natural Habitat

Exclusively found on the coarse body hair of humans, most commonly in the pubic region, but occasionally on eyelashes, eyebrows, beard, mustache, chest, or armpit hair.

Diet & Feeding

Hematophagous (feeds exclusively on human blood).

Behavior Patterns

These lice grasp coarse hairs with specialized claws that resemble crab pincers. They are relatively immobile compared to head lice but will move to feed. They lay eggs (nits) on the hair shafts.

Risks & Benefits

Risks: They cause intense itching (pruritus) due to hypersensitivity to louse saliva, which can lead to scratching and secondary bacterial skin infections. They are typically transmitted through sexual contact but can occasionally spread via shared bedding, towels, or clothing. Benefits: None known; they are obligate parasites.

Identified on: 2/12/2026