What do head lice feed on? - briefly
Head lice obtain nourishment by piercing the scalp skin and sucking the host’s blood. Their diet consists exclusively of small quantities of human blood taken several times a day.
What do head lice feed on? - in detail
Head lice survive by extracting blood from the human scalp. Their mouthparts form a piercing‑sucking apparatus that penetrates the cuticle of individual hair shafts and reaches the superficial dermal vessels. Once the skin is breached, the insect draws a small volume of plasma, typically 0.5–1 µL per feeding episode. This fluid provides all necessary nutrients, including proteins, lipids, carbohydrates, and trace minerals.
Feeding occurs several times a day. Adult females may take up to ten meals within a 24‑hour period, while nymphs feed less frequently but follow the same pattern. Each bite lasts only a few minutes before the louse withdraws its stylet. The insect does not ingest whole blood cells; instead, it filters plasma and hemoglobin, leaving the host’s skin intact except for the characteristic puncture marks.
The diet is strictly human‑derived. Head lice cannot survive on animal blood, other insects, or synthetic substrates. Their digestive enzymes are adapted to process human plasma proteins, and they lack the physiological mechanisms to process alternative food sources. Consequently, infestations are confined to individuals with direct scalp contact.
Key aspects of the feeding process:
- Attachment: Hooked claws secure the louse to a single hair strand, preventing displacement during meals.
- Penetration: The labium extends to the epidermal surface, while the mandibles pierce the cuticle.
- Suction: Muscular action creates negative pressure, drawing plasma through the foregut.
- Excretion: Excess fluid is expelled through the anus as a minute droplet, often unnoticed.
During the life cycle, each developmental stage—egg, nymph, adult—relies on the same blood source. Eggs (nits) receive nutrients indirectly through the maternal blood supply before being deposited. Nymphs molt three times, each molt requiring a fresh blood meal to support growth. Adult females require a continuous intake to produce viable eggs, typically laying 5–10 per day.
The exclusive reliance on human scalp blood explains why head lice are obligate ectoparasites and why eradication efforts focus on disrupting access to this nutrient source. Removing lice or treating the scalp eliminates the only available food, leading to rapid population decline.