Body lice, scientifically known as Pediculus humanus humanus, are parasitic insects that feed exclusively on human blood. They are distinct from head and pubic lice because they primarily reside in clothing rather than on the body. Identifying these parasites visually requires knowing their size, coloration, and preferred resting spots. Infestations are most often associated with conditions where people lack access to regular bathing and frequent changes of clean clothing. A visual inspection should focus primarily on the garments worn close to the body.
Visual Characteristics of the Adult Lice
The adult body louse is visible to the human eye, measuring between 2.3 and 4.0 millimeters in length, comparable to the size of a sesame seed. This size makes them the largest of the three types of human-infesting lice. The insect is wingless and possesses a segmented body with six legs, which it uses solely for crawling.
Coloration provides a clue as to when they last fed; when unfed, the louse appears translucent, or tan to grayish-white. Once an adult louse has consumed a blood meal, its abdomen swells slightly and takes on a reddish-brown or darker tint. Adult lice are relatively fast crawlers, but they cannot jump or fly.
The body louse must feed on blood multiple times each day to survive, making it an obligate ectoparasite. If separated from a human host for more than a couple of days, the adult louse will die.
Identifying Body Lice Eggs (Nits)
The eggs of the body louse are called nits, and they are significantly smaller than the adult insects. Nits are tiny, oval-shaped capsules that measure approximately 0.8 millimeters long. They typically appear yellowish-white or clear, and they are laid by the female louse using a strong, glue-like cement.
The female louse lays up to eight eggs per day, firmly attaching them to the fibers of clothing. This strong attachment is the primary feature that distinguishes nits from common lint or flakes of dandruff. Unlike easily brushed-off debris, nits are cemented in place and must be physically scraped away.
Nits will hatch into nymphs, which look like smaller versions of the adult louse, within about one to two weeks. The presence of these small, firmly fixed ovals indicates an active infestation.
Primary Habitats for Infestation
The primary difference between body lice and other human lice is their habitat, as they do not live directly on the body for extended periods. Body lice primarily reside and reproduce in the seams and folds of clothing, as well as in bedding. They only travel to the skin to take a blood meal, returning promptly to the shelter of the fabric.
Visual identification should focus on examining clothing, particularly the seams of garments worn close to the skin. Areas like the waistline, armpits, and groin—where clothing is tight and infrequently changed—are the most likely places to find them. Nits are almost exclusively found cemented to the fibers of these garments.
Finding the nits and crawling adults clustered along the seams of a shirt or trousers provides definitive visual evidence of a body lice infestation.