How do lice look at all stages of development? - briefly
Eggs (nits) are tiny, 0.8 mm oval structures that appear white or yellowish and are firmly attached to hair shafts close to the scalp. The three nymphal stages look like miniature adults—initially translucent, then increasingly brown and larger—with the final adult measuring 2–4 mm, flattened, gray‑brown, and bearing six legs as a nymph and eight as a mature louse.
How do lice look at all stages of development? - in detail
Lice undergo a simple metamorphosis that includes the egg, three nymphal instars, and the adult. Each stage has distinctive external features that allow identification under a magnifying lens or microscope.
The egg, commonly called a nit, is a tiny oval capsule measuring 0.5–0.8 mm in length. It is firmly attached to a hair shaft by a gelatinous cement at one pole, leaving the opposite pole free. The shell is translucent to pale yellow; as embryogenesis proceeds, it darkens to a brownish hue. The surface is smooth, lacking any visible segmentation.
The first nymphal stage emerges after about seven days of incubation. At this point the insect measures roughly 1.0 mm, is pale whitish‑gray, and possesses a proportionally large head with compound eyes that occupy most of the cephalic capsule. Antennae are short, three‑segmented, and bear sensory cones. Legs are slender, ending in claws adapted for grasping hair. The abdomen is short and unsegmented in appearance.
The second instar, reached after an additional three to four days, shows modest growth to 1.2–1.4 mm. Body coloration deepens to a light gray, and the exoskeleton becomes more sclerotized, giving a slightly glossy finish. The head remains proportionally large, but the eyes occupy a smaller relative area. Antennae lengthen marginally, and the tarsal claws become more pronounced.
The third nymph, emerging roughly three days later, measures 1.5–1.8 mm. Its color shifts to a medium gray, approaching adult pigmentation. The dorsal surface exhibits faint transverse striations. The abdomen elongates, and the genital region begins to differentiate subtly in males and females. Leg segments thicken, providing greater leverage for rapid movement.
The adult stage is attained after another three to four days. Males average 2.0–2.5 mm, females 2.5–3.5 mm. Both sexes display a uniform gray‑brown coloration; the cuticle is heavily sclerotized, giving a matte appearance. The head is reduced relative to the thorax, with well‑developed compound eyes and three‑segmented antennae bearing multiple sensilla. Thoracic legs possess robust claws and a pretarsal hook that secures the insect to hair shafts. In females, the abdomen expands posteriorly to accommodate the oviduct and developing eggs, visible as a slight bulge. Males exhibit a more tapered abdomen and a conspicuous genital capsule at the terminal segment.
These morphological markers, observed sequentially, provide a reliable framework for recognizing lice at every point of their life cycle.