How do fleas feed on human blood? - briefly
Fleas insert their needle‑like proboscis into the host’s skin, lacerating capillaries and drawing blood directly into their gut. Their saliva contains anticoagulants that keep the blood fluid while they feed.
How do fleas feed on human blood? - in detail
Fleas locate a human host by sensing heat, carbon‑dioxide, and movement. Once on the skin, the insect anchors its hind legs and begins the feeding process with a specialized mouthpart called the proboscis. The proboscis consists of a hardened, needle‑like labrum that pierces the epidermis and a flexible, tubular stylet that reaches the capillary blood vessels.
When the stylet penetrates a vessel, the flea injects saliva containing a complex mixture of pharmacologically active compounds. These include:
- Anticoagulants (e.g., apyrase) that inhibit platelet aggregation and prevent clot formation.
- Vasodilators that enlarge the blood vessel, increasing flow.
- Anesthetics that reduce the host’s perception of the bite.
The anticoagulant action maintains a steady stream of blood, allowing the flea to draw fluid through the stylet into its crop, a storage chamber in the foregut. The ingestion rate averages 0.5–1 µL per minute, depending on the species and host condition. The blood is stored temporarily, then transferred to the midgut where digestive enzymes—proteases, lipases, and carbohydrases—break down the plasma and cellular components.
During digestion, the flea assimilates amino acids, lipids, and sugars, which are used for egg development and metabolic processes. Excess fluid is excreted as a dry fecal pellet, often observed as black specks on the host’s skin. After a feeding bout lasting 5–10 minutes, the flea disengages and may reattach to continue feeding if the blood supply is insufficient.
Key physiological steps in the feeding cycle:
- Host detection via thermoreceptors and CO₂ sensors.
- Attachment using powerful hind‑leg claws.
- Penetration of skin and capillary using the proboscis.
- Saliva injection delivering anticoagulants and anesthetics.
- Blood uptake into the crop.
- Transfer to the midgut for enzymatic digestion.
- Excretion of excess fluid as feces.
The entire mechanism enables fleas to efficiently extract human blood while minimizing detection, facilitating rapid nutrient acquisition for reproduction.