The crab louse (Pthirus pubis, frequently misspelled as Phthirus pubis), also known as the pubic louse, is an insect that is an obligate ectoparasite of humans. It is typically found in pubic hair, but may also live on other areas with hair, including the eyelashes. They feed exclusively on blood. Humans are the only known hosts of this parasite, although a closely related species, Pthirus gorillae, infects gorilla populations. The species passed to humans 3.3 million years ago. An adult crab louse is about 1.3-2 mm long (rather smaller than the body louse and head louse), and can be distinguished from those other species by its almost round body.
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