How can lice be distinguished? - briefly
Lice are identified by species‑specific morphology—body length, coloration, and claw shape—and by the area of the host they inhabit (head, body, or pubic region). The presence of nits firmly attached to hair shafts confirms an infestation.
How can lice be distinguished? - in detail
Lice identification relies on a combination of morphological traits, host specificity, and egg placement.
Adult head lice (Pediculus humanus capitis) measure 2–3 mm, have a dorsally flattened body, and lack wings. Their coloration ranges from gray‑white to brown, often darkening after a blood meal. Antennae are short, with five segments, and the thorax bears six legs, each ending in a claw adapted for grasping hair shafts.
Body lice (Pediculus humanus humanus) are slightly larger, 3–4 mm, and exhibit a broader, more robust abdomen. Their coloration is similar to head lice, but they tend to appear more pigmented. Unlike head lice, they live primarily in clothing seams and lay eggs on fabric fibers rather than on hair.
Pubic lice (Phthirus pubis), also called crab lice, are markedly different in shape. They are 1–2 mm long, with a broad, crab‑like body and large, clawed front legs that grasp coarse hair. Their color varies from light brown to dark brown.
Eggs (nits) provide additional clues. Head‑lice nits are firmly attached to the base of hair shafts, about 1 mm from the scalp, and have a characteristic oval shape with a pointed operculum. Body‑lice nits are found on seams of garments, often embedded in fabric fibers. Pubic‑lice nits are attached to the base of pubic hair, appearing more rounded and less firmly cemented.
Microscopic examination can reveal finer distinctions:
- Head lice: short, robust maxillae; antennal segments 1–5 gradually enlarging.
- Body lice: elongated maxillae; antennal segments 1–5 more uniform in size.
- Pubic lice: enlarged, hooked fore‑legs; reduced mouthparts.
Molecular methods, such as PCR amplification of mitochondrial COI gene, allow precise species confirmation when visual traits overlap or specimens are damaged.
In practice, accurate differentiation combines visual assessment of size, body shape, leg morphology, and egg location with, when necessary, laboratory analysis for definitive species identification.