Why do lice bite? - briefly
Lice bite to obtain blood, which supplies the nutrients necessary for their growth and reproduction. Their saliva contains anticoagulants that trigger itching and inflammation in the host.
Why do lice bite? - in detail
Lice require blood to complete their life cycle; the act of biting provides the necessary nutrients. Saliva injected during feeding contains anticoagulants that prevent clotting, allowing continuous extraction of blood from the host’s skin. This process also introduces proteins that trigger an inflammatory response, producing itching and redness.
Key physiological factors:
- Nutrient demand: Nymphs and adults need hemoglobin and plasma proteins for growth and egg production.
- Sensory adaptation: Mouthparts are equipped with mechanoreceptors that detect temperature and carbon‑dioxide gradients, guiding the insect to optimal feeding sites.
- Salivary composition: Enzymes such as apyrase and anticoagulant peptides maintain fluid flow, while histamine‑releasing substances provoke host irritation, which may aid in dispersal when the host scratches.
The feeding cycle typically follows these steps:
- Location: Louse climbs onto the scalp or body hair, seeking a region with abundant capillaries.
- Attachment: Hooked claws secure the insect to a single hair shaft, preventing dislodgement.
- Penetration: The louse inserts its stylet into the epidermis, reaching the superficial dermal vessels.
- Extraction: Blood is drawn continuously for several minutes before the insect withdraws and relocates.
Host reactions vary with individual sensitivity; repeated bites can lead to secondary infection if the skin barrier is broken. Effective control measures focus on eliminating the parasite and reducing the opportunity for blood feeding, thereby interrupting the cycle that drives the biting behavior.