How to identify which lice? - briefly
Examine the parasite’s size, body shape, and claw configuration, then note the infestation site: head‑lice are 2–3 mm, wingless, and attach to hair shafts close to the scalp, whereas body‑lice are 3–5 mm, possess wings, and live in clothing seams.
How to identify which lice? - in detail
Identifying the specific type of lice requires a systematic approach that combines visual inspection, knowledge of habitat preferences, and, when necessary, laboratory analysis.
First, collect a sample from the affected individual or animal. Use a fine-toothed comb or a lice detection device to isolate live insects. Place the specimens on a white surface for clear observation.
Examine morphological features with a magnifying lens (10–20×) or a stereomicroscope. Key characteristics include:
- Body size: head lice (Pediculus humanus capitis) measure 2–3 mm; body lice (Pediculus humanus corporis) are slightly larger, 3–4 mm; crab lice (Pthirus pubis) are broader, 1.5–2 mm.
- Body shape: head and body lice are elongated and flattened, while crab lice are crab‑shaped with a wider posterior.
- Head orientation: head lice have a forward‑pointing head; body lice have a backward‑pointing head; crab lice have a laterally oriented head.
- Antennae length: head lice possess longer antennae relative to body size; body lice have shorter antennae; crab lice have very short antennae.
- Legs: head and body lice have six legs of equal length; crab lice have robust hind legs adapted for grasping hair shafts.
Second, consider the location of infestation. Head lice are confined to scalp hair, especially behind the ears and at the nape. Body lice inhabit clothing seams and lay eggs on fabric, moving to the skin only to feed. Crab lice colonize coarse hair in the pubic region, eyebrows, eyelashes, or facial hair.
Third, assess the appearance of eggs (nits). Head lice nits are firmly attached to hair shafts within 1 cm of the scalp and have a characteristic oval shape. Body lice nits are found on clothing fibers, often near seams. Crab lice nits are larger, attached to coarse hair, and may appear more spherical.
If visual identification remains uncertain, submit specimens to a parasitology laboratory. Microscopic slides prepared with cleared specimens allow confirmation of species based on setae patterns, genitalia structure, and spiracle configuration. Molecular methods, such as PCR amplification of mitochondrial COI gene, provide definitive species identification when morphology is ambiguous.
Finally, document findings: record size measurements, morphological traits, infestation site, and any laboratory results. Accurate identification guides appropriate treatment protocols and informs public‑health interventions.