Hematophagy, the practice of feeding on blood, has evolved independently across numerous animal groups, establishing a unique and specialized niche. This dietary adaptation allows organisms to exploit a resource readily available inside a host’s body. Blood provides an extremely rich and concentrated meal, containing high levels of protein and iron. For many small animals, accessing this liquid tissue is energetically more efficient than hunting or digesting solid food. This strategy necessitates specialized adaptations to locate a host and overcome defenses, such as blood clotting.
Flying and Jumping Insects
Many familiar blood-feeders belong to the insect class, often employing rapid, hit-and-run feeding tactics. Mosquitoes, for example, use a modified proboscis, a sheath containing six needle-like stylets. The female mosquito uses these stylets to saw into the skin and locate a capillary, injecting saliva containing anticoagulants and local anesthetics for an undetected feed. This blood meal is typically an obligatory requirement for the female to produce viable eggs.
Fleas, which are wingless insects built for jumping, possess piercing-sucking mouthparts composed of three stylets that work together. Two outer stylets saw into the skin, and a third stylet forms the feeding tube through which the blood is drawn. Like mosquitoes, fleas inject saliva with anticoagulants to maintain blood flow, and a single female can consume nearly 18% of her body weight in blood per meal.
Other insects, such as black flies and tsetse flies, are considered telmophages because they lacerate the host’s skin and feed on the pool of blood that collects at the bite site. These biting flies use their mouthparts to create a wound, relying on the ensuing bleed for their meal. Female flies from these groups often require the protein-rich blood to mature their eggs.
The Persistent Parasites
Unlike quick-feeding insects, hematophagous arachnids such as ticks and certain mites employ a strategy of prolonged attachment to their hosts. Ticks are obligate blood-feeders throughout their larval, nymphal, and adult stages, requiring a blood meal during each phase. They are known as “pool feeders” because they anchor themselves to the host for days or even weeks.
To maintain this extended attachment, hard ticks secrete a cement-like substance around their specialized mouthparts, which include a barbed structure called the hypostome. This cement chemically bonds them to the host’s skin, resisting removal while they slowly engorge. Their feeding process involves an alternating pattern of salivating anti-clotting agents and sucking, making them highly efficient at extracting a large volume of blood over a multi-day period.
Mites, including chiggers and scabies mites, represent a persistent group of arachnid parasites. Chiggers, specifically the larval stage, do not burrow but instead inject digestive enzymes that break down host tissue, feeding on the resulting liquefied material and lymph. Scabies mites, in contrast, burrow into the skin to feed on tissue and fluid, maintaining a close, prolonged parasitic relationship with the host.
Aquatic and Terrestrial Worms
The phylum Annelida includes segmented worms, with leeches being the most recognizable hematophagous members. The majority of these species live primarily in freshwater, though terrestrial and marine varieties also exist. They use a small anterior sucker, which contains the mouth, and a larger posterior sucker for movement and attachment to the host.
The medicinal leech, Hirudo medicinalis, uses three jaws lined with sharp teeth to create a characteristic Y-shaped incision in the host’s skin. During feeding, the leech secretes a complex cocktail of bioactive substances from its salivary glands. The most notable is hirudin, a powerful polypeptide anticoagulant that prevents clotting, allowing the leech to consume a large meal that can take months to digest. Hirudin and other compounds are studied and utilized today for their anticoagulant and anti-inflammatory properties in medicine.
Mammals and Fish
While hematophagy is most common in invertebrates, a few specialized vertebrates have also adopted this diet. The common vampire bat (Desmodus rotundus) is the only mammal that feeds exclusively on blood. The bat does not suck blood but uses razor-sharp teeth to make a clean, shallow slice in the host’s skin.
The bat then laps up the flowing blood using a specialized tongue with lateral grooves, relying on capillary action to draw the blood into its mouth. Their saliva contains an anesthetic to prevent the host from waking and a potent anticoagulant, such as the enzyme Draculin, to keep the blood flowing during the 20-30 minute meal.
In aquatic environments, certain species of lampreys, an ancient group of jawless fish, are blood-feeders. The adult parasitic lamprey uses its large, circular mouth, lined with keratinous teeth, to attach firmly to a larger fish. A rasping tongue then drills a hole into the host’s flesh, and the lamprey feeds on the blood and body fluids. Lampreys secrete an anticoagulant to maintain the flow of blood from their host.