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Kunstformen der Natur (1904) by Ernst Haeckel
Kunstformen der Natur (1904) by Ernst Haeckel

Hematophagy (sometimes spelled haematophagy or hematophagia) is the practice by certain animals of feeding on blood (from the Greek words αἷμα haima "blood" and φάγειν phagein "to eat"). Since blood is a fluid tissue rich in nutritious proteins and lipids that can be taken without great effort, hematophagy has evolved as a preferred form of feeding for many small animals, such as worms and arthropods. Some intestinal nematodes, such as Ancylostomids, feed on blood extracted from the capillaries of the gut, and about 75 percent of all species of leeches (e.g., Hirudo medicinalis), a free-living worm, are hematophagous. Some fish, such as lampreys and candirus, and mammals, especially the vampire bats, and birds, such as the vampire finches, hood mockingbirds, the Tristan thrush, and oxpeckers also practise hematophagy.

Mechanism and evolution

These hematophagous animals have mouth parts and chemical agents for penetrating vascular structures in the skin of hosts, mostly of mammals, birds, and fish. This type of feeding is known as phlebotomy (from the Greek words, phleps "vein" and tomos "cutting").

Once phlebotomy is performed (in most insects by a specialized fine hollow "needle," the proboscis, which perforates skin and capillaries; in bats by sharp incisor teeth 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 evolved hembiochemical 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 males feed on pollen and fruit juice (only) while the females survive strictly by feeding on mammalian blood. 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 flies) 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. 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, CO2, heat, light, movement, etc.

See also

Unless indicated otherwise, the text in this article is either based on Wikipedia article "Hematophagy" or another language Wikipedia page thereof used under the terms of the GNU Free Documentation License; or on original research by Jahsonic and friends. See Art and Popular Culture's copyright notice.

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