Body lice (Pediculus humanus humanus) are parasitic insects that feed exclusively on human blood. They are a different subspecies from head lice and pubic lice, possessing distinct habits that make their visual identification unique. Understanding their physical characteristics and habitat is the most direct way to confirm their presence.
Size and Appearance of the Adult Louse
A fully grown body louse measures between 2.3 and 3.6 millimeters long, about the size of a sesame seed. They have an elongated, oblong shape and six legs adapted for grasping clothing fibers. When unfed, the louse is pale gray, tan, or whitish, providing camouflage against fabric.
The insect’s appearance changes after feeding. Following a blood meal, the abdomen becomes engorged, shifting the color to a darker reddish-brown. This temporary change makes them easier to spot visually when moving across the skin or fabric. They are large enough to be seen with the naked eye, though a magnifying lens can aid confirmation.
Identifying Eggs and Nymphs
The eggs, commonly called nits, are the first immature stage. These are tiny, oval structures, measuring about 0.8 millimeters long, and are firmly cemented to fabric fibers. Nits appear yellowish-white and are most often found clustered in the seams of clothing.
When a nit hatches, the immature louse, called a nymph, emerges. Nymphs resemble adults but are significantly smaller, starting at the size of a pinhead. They are translucent, making them harder to detect than adults or nits. Nymphs grow progressively larger through three molting stages until they reach adult size, feeding on blood to mature.
Where Body Lice Live
The primary distinction of body lice is their preferred dwelling and egg-laying location. They do not primarily live on the human body; instead, they reside and lay nits almost exclusively in the seams, folds, and stitches of clothing and bedding. This behavior is common in garments that are worn constantly and infrequently washed.
The louse only migrates to the skin surface to take a blood meal, making its presence on the body transient. Finding live lice or nits in the inner seams of clothing is the definitive visual confirmation of an infestation. Favored locations for nits are typically where clothing seams contact the skin, such as the waistline and armpits.
Visual Signs of an Infestation
The presence of body lice is often first indicated by reactions on the skin. Small, localized red dots are visible bite marks showing where the louse has fed. These bites can cause generalized skin irritation or a rash due to an allergic reaction to the louse saliva.
Consistent, intense scratching leads to secondary visual evidence. In prolonged infestations, heavily bitten areas, particularly around the midsection and groin, may become thickened and darkened. This chronic condition is sometimes referred to as melanoderma or “vagabond’s disease.”