How and from what do lice become attached? - briefly
Lice cling to a host by gripping individual hairs or fibers with their curved tarsal claws and by anchoring their mouthparts in the skin to feed. Attachment occurs directly on the scalp, body hair, or clothing, where the insects find suitable anchoring points.
How and from what do lice become attached? - in detail
Lice secure themselves to a host through a combination of mechanical grip and biochemical adhesion. The primary mechanical method involves the tarsal claws on each leg, which interlock with the cylindrical shape of hair shafts, beard hairs, or the fibers of clothing. The claws fit snugly around the hair or fiber, preventing displacement by movement or grooming. In addition, the ventral surface of the claws bears microscopic setae that increase friction and enhance stability.
Biochemical adhesion occurs during oviposition. Female lice secrete a proteinaceous cement from specialized glands located near the abdomen. This cement hardens within seconds, anchoring each egg (nits) to the base of the hair shaft or to fabric fibers. The cement is resistant to water and most detergents, allowing eggs to remain attached through washing and moisture exposure.
Attachment sources differ among species:
- Head lice (Pediculus humanus capitis): Attach to scalp hair, particularly near the nape, behind the ears, and at the crown. The dense, fine hair provides optimal grip for claws.
- Body lice (Pediculus humanus corporis): Attach to the seams of clothing, especially where fabric is tightly woven. The insects reside in the folds and creases, using claws to hold onto fibers.
- Pubic lice (Pthirus pubis): Attach to coarse pubic hair and other body hair with a larger, broader claw arrangement adapted to thicker shafts.
The attachment process follows a consistent sequence:
- Crawling: Newly emerged nymphs move across the host’s surface by alternating leg movements, searching for a suitable anchoring point.
- Gripping: Upon locating a hair or fiber, the front pair of legs extend, the claws close around the shaft, and the remaining legs stabilize the position.
- Feeding: The louse inserts its piercing‑sucking mouthparts into the epidermis, releasing saliva that contains anticoagulant compounds to maintain blood flow.
- Reproduction: After a blood meal, the female positions herself near a hair or fiber, deposits an egg, and applies cement to secure it.
- Egg attachment: The cement cures, fixing the nit in place until hatching, after which the nymph repeats the crawling‑gripping cycle.
Environmental factors influence attachment efficiency. High humidity softens hair shafts, allowing tighter claw closure, while low humidity can cause hair to become more rigid, reducing grip. Temperature affects metabolic rate; optimal temperatures (30–32 °C) accelerate feeding and reproduction, leading to stronger attachment activity.
Control measures target these mechanisms. Mechanical removal (combing) disrupts the claw grip, while chemical agents (e.g., permethrin) impair the louse’s nervous system, reducing its ability to maintain attachment. Detergents with surfactants can dissolve the cement, facilitating nits removal from hair or fabric.
Understanding the precise methods of mechanical and biochemical adhesion provides a basis for effective eradication strategies and informs public‑health recommendations for preventing infestations.