What is the size of a louse in centimeters? - briefly
A human louse measures approximately 0.2–0.4 cm in length, varying by species and developmental stage. Adult head lice average around 0.3 cm, while nymphs are slightly shorter.
What is the size of a louse in centimeters? - in detail
The adult head louse (Pediculus humanus capitis) measures approximately 2.5 mm in length and 0.8 mm in width, which corresponds to 0.25 cm × 0.08 cm. Body lice (Pediculus humanus corporis) are slightly larger, averaging 3.0 mm long and 1.0 mm wide (0.30 cm × 0.10 cm). Pubic lice (Pthirus pubis) differ in shape; they are about 2.0 mm long and 1.2 mm wide (0.20 cm × 0.12 cm).
Size varies with developmental stage. Nymphs progress through three instars before reaching adulthood:
- First‑instar nymph: 1.0 mm (0.10 cm) long
- Second‑instar nymph: 1.5 mm (0.15 cm) long
- Third‑instar nymph: 2.0 mm (0.20 cm) long
Adult females are typically 10 % larger than males, reflecting the need to accommodate eggs.
Measurements are obtained using a calibrated ocular micrometer attached to a light microscope. Specimens are placed on a slide with a drop of water or ethanol, and the micrometer scale is aligned with the louse’s longest axis for length and with the widest point for breadth. Repeated readings from multiple individuals provide the average dimensions reported above.
Environmental factors such as host body temperature, humidity, and availability of blood meals can cause minor fluctuations in size, but the ranges given remain consistent across most human populations.