Hematophagy (sometimes spelledhaematophagy orhematophagia) is the practice by certainanimals offeeding onblood (from theGreek words αἷμαhaima "blood" and φαγεῖνphagein "to eat"). Since blood is a fluid tissue rich in nutritiousproteins andlipids that can be taken without great effort, hematophagy is a preferred form of feeding for many small animals, such asworms andarthropods. Some intestinalnematodes, such asAncylostomatids, feed on blood extracted from thecapillaries of the gut, and about 75 percent of all species ofleeches (e.g.,Hirudo medicinalis) are hematophagous. The spiderEvarcha culicivora feeds indirectly on vertebrate blood by specializing on blood-filled female mosquitoes as their preferred prey.[1] Somefish, such aslampreys andcandirus;mammals, especiallyvampire bats; and birds, including thevampire finch,Hood mockingbird,Tristan thrush, andoxpeckers, also practise hematophagy.
Hematophagous animals havemouth parts and chemical agents for penetrating vascular structures in the skin ofhosts, mostly of mammals, birds, and fish. This type of feeding is known asphlebotomy (from the Greek words,phleps "vein" andtomos "cutting").
Once phlebotomy is performed (in most insects by a specialized fine hollow "needle", theproboscis, which perforates skin andcapillaries; in bats by sharpincisor 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 naturalhemostasis (blood coagulation),vasoconstriction, inflammation, and pain sensation in the host, hematophagous animals haveevolved chemical solutions, in their saliva for instance, that they pre-inject—andanesthesia and capillary dilation have evolved in some hematophagous species. Scientists have developedanticoagulant medicines from studying substances in the saliva of several hematophagous species, such as leeches (hirudin).
Hematophagy is classified as eitherobligatory orfacultative. Obligatory hematophagous animals cannot survive on any other food. Examples includeRhodnius prolixus, a South Americanassassin bug, andCimex 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 asAedes 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 asLeptoconops torrens can also be facultative hematophages. Inanautogenous 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 asflies) 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 genusCalyptra. Hematophagy in insects, including mosquitoes, is thought to have arisen from phytophagous or entomophagous origins.[2][3][4][5] Several complementarybiological 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 forsweat components,CO2, 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 mosquitoAedes 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 asvitellogenin, which is a yolk protein used for egg production.[6]
The phlebotomic action opens a channel for contamination of the host species withbacteria,viruses and blood-borneparasites contained in the hematophagous organism. Thus, many animal and humaninfectious diseases are transmitted by hematophagous species, such as thebubonic plague,Chagas disease,dengue fever,eastern equine encephalitis,filariasis,leishmaniasis,Lyme disease,malaria,rabies,sleeping sickness,St. Louis encephalitis,tularemia,typhus,Rocky Mountain spotted fever,West Nile fever,Zika fever, and many others.
Insects andarachnids of medical importance for being hematophagous, at least in some species, include thesandfly,blackfly,tsetse fly,bedbug,assassin bug,mosquito,tick,louse,mite,midge, andflea.
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.[citation needed] 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 calleddesmoteplase based on the saliva ofDesmodus rotundus (a vampire bat) was shown to improve recovery instroke patients.[7]
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Many human societies also drink blood or use it to manufacture foodstuffs and delicacies. Cow blood mixed withmilk, for example, is a mainstay food of the AfricanMaasai. Many places around the world eatblood sausage. Some societies, such as theMoche, had ritual hematophagy, as well as theScythians, a nomadic people ofEastern Europe, who drank the blood of the first enemy they killed inbattle. Psychiatric cases of patients performing hematophagy also exist. Sucking or licking one's own blood from a wound to clean it is also a common human behavior[dubious –discuss], and in small enough quantities is not considered taboo. Finally, humanvampirism has been a persistent object of literary and cultural attention.[citation needed]
