Lice are small, wingless insects that live as parasites on humans, feeding on blood. They adapt to live on different parts of the body, and their presence requires careful visual inspection for identification. Understanding the appearance of the adults and their eggs is necessary for proper identification, which is the first step toward effective treatment.
The True Color of Adult Lice
An adult louse is roughly the size of a sesame seed and initially appears translucent, grayish-white, or tan. This neutral tone allows the insect to blend into the host’s hair or skin, making it difficult to spot. The louse has an elongated body and six legs with specialized claws designed to firmly grasp the hair shaft. This standard coloration is most visible when the insect has not recently fed on blood.
The louse’s appearance changes dramatically after a successful blood meal, which they must take multiple times a day. As the insect ingests blood, its body swells slightly, and the abdomen becomes noticeably darker. A recently fed adult louse will appear reddish-brown or nearly black due to the human blood filling its digestive tract. This temporary color change makes the insect easier to spot against lighter skin or hair.
Nits: Appearance and Location
Lice eggs, commonly referred to as nits, are often the first sign of an infestation. A viable nit is tiny, comparable in size to a pinpoint, and is typically oval-shaped. Before hatching, nits usually appear translucent, yellowish, or light tan. The female louse secretes a powerful, waterproof, glue-like substance to cement the nit firmly to the base of a hair shaft, usually within a quarter-inch of the scalp for incubation warmth.
Once the nymph emerges, the empty egg casing remains attached to the hair, changing to a duller white or clear color. This empty shell moves away from the scalp as the hair grows, sometimes leading to confusion with common scalp debris. The key difference from substances like dandruff is the strength of the adhesion; a true nit cannot be easily brushed away. Finding a nit close to the scalp indicates a possible active infestation, as the warmth near the skin is necessary for them to hatch.
Head, Body, and Pubic Lice Differences
The general coloring of all human lice species is similar, ranging from grayish-white to blood-filled reddish-brown. However, their preferred location and body shape provide the most significant identification differences. Head lice (Pediculus humanus capitis) are the most common species, measuring 2 to 3 millimeters long, and are found almost exclusively on the hair and scalp.
Body lice (Pediculus humanus humanus) are morphologically almost identical to head lice but are slightly larger, measuring up to 3.6 millimeters. These insects reside and lay their eggs in the seams of clothing, only moving to the skin to feed.
The third species, pubic lice (Pthirus pubis), often called “crabs,” presents the most unique morphology. These lice are the smallest, measuring 1.1 to 1.8 millimeters, and have a noticeably wider, rounded body shape, giving them a crab-like appearance. Pubic lice primarily infest the coarser hairs of the pubic region, though they can be found in other coarse body hair, such as the armpits or eyebrows.