Feeding on the blood of another animal is a way of life found in many groups of animals, and it is one way of passing diseases to humans, their livestock and their pets.
Arthropods
14,000 species of arthropod suck blood for a living, and many of them attack humans and transmit important diseases. Mosquitoes, Ticks and Assassin Bugs are among the most well-known, together with fleas, lice and bedbugs, but there many others, including mites, midges, and even some moths. They all have special senses to enable them to locate their host, often the ability to detect carbon dioxide, and body-heat if the host is a warm-blooded bird or mammal.
Leeches
One group of annelid worms (the leeches) includes a few species that feed on vertebrate blood. The Medicinal Leech Hirudo medicinalis was once used to ‘let blood’ - when it was thought that too much blood was a ‘bad thing’ – and it continues to be used in modern medicine. It is particularly useful after plastic surgery and to stimulate blood flow when ears, eyelids, fingers etc. have been re-attached or grafted on. The Medicinal Leech is now becoming an endangered species in the wild, so it is being reared in ‘leech farms’ around the world.
Fish
Lampreys are not true fish, but they are closely related. There are about 40 species worldwide, with most living in freshwater and coastal seas. Typically the eggs hatch in freshwater and the larvae live in the mud ‘filter-feeding’ on micro-organisms. After a number of years as larvae they undergo a ‘metamorphosis’ and change into the very different adult form. The adults suck the blood of fish. They are supposed to taste very ‘meaty’ and have been caught and eaten for centuries. King Henry of England reputedly died from ‘a surfeit of lampreys’!
Mammals
Vampire Bats all live in South America. There are three species; the Common Vampire Bat Desmodus rotundus, the Hairy-legged Vampire Bat Diphylla ecaudata and the White-winged Vampire Bat Diaemus youngi. The Common Vampire Bat is the one that most frequently attacks humans, while the other two seem to prefer birds. In fact these bats do not seem to be fond of the taste of human blood, and it is only a ‘second choice’. The bad news is that their bite can transmit the rabies virus, and the good news is that studying their saliva has led to the development of a drug (desmoteplase) which is proving useful in the treatment of strokes.
Birds
It has recently been realised that the Oxpeckers of Africa like to drink the blood of the animal whose ticks they are supposed to be removing as well as eating the blood-filled ticks themselves. This gruesome habit is shared by the Vampire Finch of the Galapagos Islands who is rather partial to the blood of Boobies and other daft seabirds. In both cases this habit is evolving from a pre-existing 'cleaner' role, where the bird was accepted because it was providing a useful service.
Humans
Before we become too disgusted by these ‘blood-sucking’ habits it is as well to remember that most of us will suck a cut finger, and many enjoy ‘black pudding’!
see also 'animal senses'
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