How do lice run across? - briefly
Lice move by crawling; they alternately lift and push forward with their six legs, using tiny claws to grip hair shafts. Their locomotion is a slow, deliberate progression rather than a true run.
How do lice run across? - in detail
Lice locomotion relies on three pairs of articulated legs equipped with clawed tarsi that grip hair shafts, feathers, or fabric fibers. Each leg moves independently, producing a tripod gait: while two legs on one side push forward, the opposite leg on the other side provides support, allowing continuous forward motion without loss of attachment.
The movement cycle consists of four phases:
- Protraction: the leg extends forward, the claw hooks onto the next filament.
- Grip: sensory receptors confirm secure contact, then flexor muscles engage.
- Retraction: the leg pulls the body toward the anchored point.
- Release: the claw disengages, preparing for the next protraction.
Muscular control is mediated by a ventral nerve cord that coordinates rhythmic bursts, ensuring timing between left and right leg pairs. The thoracic exoskeleton houses powerful muscles that generate the force required to overcome friction and the elasticity of host hair.
Speed varies with species and substrate. Human head lice (Pediculus humanus capitis) achieve average velocities of 0.2 mm s⁻¹ on scalp hair, while body lice (Pediculus humanus humanus) can reach up to 0.5 mm s⁻¹ on clothing fibers. Acceleration is limited by the need to maintain grip; sudden changes in direction are achieved by rapid reorientation of the front legs rather than by body rotation.
Environmental factors influence locomotion:
- Moisture: humid conditions soften hair cuticles, facilitating claw penetration.
- Temperature: optimal activity occurs between 28 °C and 32 °C; lower temperatures reduce muscle contraction speed.
- Surface texture: fine, flexible fibers provide better anchorage than coarse, rigid materials.
Lice also display occasional “jumping” behavior, not true leaps but rapid releases and re‑attachments that allow them to traverse short gaps between hairs. This maneuver is generated by simultaneous contraction of all six legs, propelling the body forward a few millimetres before re‑establishing grip.
Overall, lice movement combines precise mechanical grip, coordinated neural patterns, and adaptations to host microenvironments, enabling efficient traversal across hair, feathers, or fabric.