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Hematophagy (sometimes spelled haematophagy or hematophagia) is the practice by certain of feeding on blood (from the Ancient Greek words αἷμα haima "blood" and φαγεῖν phagein "to eat"). Since blood is a fluid tissue rich in nutritious and that can be taken without great effort, hematophagy is a preferred form of feeding for many small animals, such as and . Some intestinal parasitic worm, such as Ancylostomatidae, feed on blood extracted from the Capillary of the gut, and about 75 percent of all species of (e.g., Hirudo medicinalis) are hematophagous. The spider Evarcha culicivora feeds indirectly on vertebrate blood by specializing on blood-filled female mosquitoes as their preferred prey. Some fish, such as and candirus; , especially ; and birds, including the vampire finch, Hood mockingbird, Tristan thrush, and oxpeckers, also practise hematophagy.
Once phlebotomy is performed (in most insects by a specialized fine hollow "needle", the proboscis, which perforates skin and capillary; in bats by sharp incisor that act as a razor to cut the skin), blood is acquired either by sucking action directly from the veins or capillaries, from a pool of escaped blood, or by lapping (again, in bats). To overcome natural hemostasis (blood coagulation), vasoconstriction, inflammation, and pain sensation in the host, hematophagous animals have evolution chemical solutions, in their saliva for instance, that they pre-inject—and anesthesia and capillary dilation have evolved in some hematophagous species. Scientists have developed anticoagulant medicines from studying substances in the saliva of several hematophagous species, such as leeches (hirudin).
Hematophagy is classified as either obligatory or facultative. Obligatory hematophagous animals cannot survive on any other food. Examples include Rhodnius prolixus, a South American assassin bug, and Cimex lectularius, the human bed bug. Facultative hematophages, meanwhile, acquire at least some portion of their nutrition from non-blood sources in at least one of the sexually mature forms. Examples of this include many mosquito species, such as Aedes aegypti, whose both males and females feed on pollen and fruit juice for survival, but the females require a blood meal to produce their eggs. Fly species such as Leptoconops torrens can also be facultative hematophages. In anautogenous species, the female can survive without blood but must consume blood in order to produce eggs (obligatory hematophages are by definition also anautogenous).
As a feeding practice, hematophagy has evolved independently in a number of arthropod, annelid, nematode and mammalian taxa. For example, Diptera (insects with two wings, such as fly) have eleven families with hematophagous habits (more than half of the 19 hematophagous arthropod taxa). About 14,000 species of arthropods are hematophagous, even including some genera that were not previously thought to be, such as moths of the genus Calyptra. Hematophagy in insects, including mosquitoes, is thought to have arisen from phytophagous or entomophagous origins. (2025). 9780511115530, Cambridge University Press. ISBN 9780511115530 Several complementary biological adaptations for locating the hosts (usually in the dark, as most hematophagous species are nocturnal and silent to avoid detection) have also evolved, such as special physical or chemical detectors for sweat components, carbon dioxide, heat, light, movement, etc.
In addition to these biological adaptations that have evolved to help blood-feeding arthropods locate hosts, there is evidence that RNA from host species may also be taken up and have regulatory consequences in blood feeding insects. A study on the yellow fever mosquito Aedes aegypti has shown that human blood microRNA has-miR-21 are taken up during blood feeding and transported into the fat body tissues. Once in the fat body they target and regulate mosquito genes such as vitellogenin, which is a yolk protein used for egg production.
Insects and arachnids of medical importance for being hematophagous, at least in some species, include the sandfly, Black fly, tsetse fly, Cimex, assassin bug, mosquito, tick, louse, mite, midge, and flea.
Hematophagous organisms have been used by physicians for beneficial purposes (hirudotherapy). Some doctors now use leeches to prevent the clotting of blood on some wounds following surgery or trauma. The anticoagulants in the laboratory-raised leeches' saliva keeps fresh blood flowing to the site of an injury, actually preventing infection and increasing chances of full recovery. In a recent study a genetically engineered drug called desmoteplase based on the saliva of Desmodus rotundus (a vampire bat) was shown to improve recovery in stroke patients.
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