How does a blood‑filled louse look? - briefly
An engorged louse appears markedly swollen, with its abdomen expanded and taking on a deep red‑brown to almost black hue. The body becomes broader and more opaque, contrasting with the lighter, flatter appearance of an unfed specimen.
How does a blood‑filled louse look? - in detail
An engorged louse exhibits a markedly swollen abdomen that can increase the insect’s overall length by up to 50 %. The body becomes rounded and balloon‑like, especially the posterior segments, while the anterior region (head and thorax) retains its usual compact shape.
- Color: The cuticle turns dark reddish‑brown to almost black as hemoglobin fills the hemocoel. In some species the hue may appear glossy due to the tension of the stretched exoskeleton.
- Size: Typical adult lice range from 2 to 4 mm; when fully distended they may reach 5–6 mm.
- Abdomen: The ventral surface bulges outward, creating a convex profile. The dorsal plates are stretched, often revealing fine striations or punctate patterns that were less visible in an unfed state.
- Legs and claws: Legs remain proportionally short; claw tips appear more splayed as the body expands, but their structure does not change.
- Head and mouthparts: The head stays relatively unchanged, with the proboscis or mandibles positioned for piercing. The antennae may appear slightly retracted toward the thorax due to the pressure of the swollen abdomen.
- Surface texture: The cuticle becomes taut, giving a smoother, slightly reflective appearance. In some cases, the thinness of the cuticle allows the underlying blood to be partially visible through the exoskeleton, creating a semi‑transparent effect.
Overall, a blood‑laden louse is easily distinguished from an unfed individual by its enlarged, darkened abdomen, increased length, and a tighter, glossier exoskeleton.