Category: Feeding Behavior.
With movies and books like Twilight, blood suckers have been given the spotlight. Hematophagy is the practice of certain animals of feeding on blood only. These animals have evolved from a need in many small animals to be able to have access to nutritious food without much effort. Blood is the key of life, and for some animals, this holds more truth.
An Anopheles stephensi mosquito feeding on human blood. © CDC.
Most people are aware of the term phlebotomy, which is the process of making an incision in a vein, as a practice associated with doctors and hospitals. It is from hematophagous animals that physicians got the idea in the first place. There are certain characteristics common to all hematophagous animals. Chief among them is the use of a chemical agent as an anesthetic in the area in which they will feed and a proboscis. The proboscis is a fine, hollow and needle-like protrusion which the channel uses to penetrate skin and capillaries. In the case of bats, in place of a proboscis, you will find two sharp incisors. The bat then either laps or saws the blood from its victim.
Butterflies sucking fresh blood from a sock. © Túrelio.
But blood can clot
One of the properties of blood that these animals had to evolve to overcome is its tendency to clot. Most of these animals have a biochemical solution in their saliva that they bathe the area with before attempting to feed. This substance overcomes vasoconstriction, inflammation and pain so that the host generally doesn’t know it has been a meal until it’s all over. Modern anesthesia and capillary dilation techniques got their start from these animals, and the compounds used are based on substances found in the saliva of such species as leeches and bats.
A vampire bat feeding on an animal. © Sandstein.
Two categories of hematophagy
Scientists have labeled two categories of hematophagy, optional practice or obligatory practice. Optional means that the animal will eat other things besides blood. While most people see mosquitoes as only a bloodsucking nuisance. They also the fruit juice, pollen and other biological food fluids. Most often, the mosquitoes use blood of several other types of animals, such as coyotes and other members of the canine family. An example of obligatory hematophagy would be the assassin bug of South America, which only eats blood.
Not all species in a genus practices hematophagy
Over the centuries, hematophagy has evolved in some very surprising ways. It has evolved independently in many species like arthropods, annelids, nematodes and mammals. Not every genus within a species will display this behavior. For instance in the category diptera (insects with two wings), like flies and gnats, there are 11 families or genera that exhibit hemophagous tendencies. There is also evidence that suggest that some adaptations evolved to hunt at night. This better enables them to feed unmolested.
Bedbug feeding on human blood. © CDC and WHO.
Humans eat blood too
While not wildly popular anymore in civilized countries, there are still throwbacks. There are still foodstuffs and delicacies prepared from the blood of animals. The Masai people of Africa still use blood mixed with milk as a staple in their diets. Black pudding is eaten around the world, as is blood sausage, and these are made from blood. Many religious rituals require the participants to drink blood. The sacrament in Christianity pays homage to this type of ritual. There are those that practice vampirism, although it is nothing quite as glamorous as Hollywood makes it out to be and is taboo in most societies. It is treated as an aberration and mental defect.
Its common in nature
It is easy to go ugh when thinking of sustaining life by consuming blood but bear in mind that we humans kill other animals and eat their flesh. These animals are vilified in movies and fictional literature but if you put it into perspective, which is less harmful to the other species? Sneaking a bit of blood that leaves the host unscathed or permanent death and dismemberment?
More on hematophagy: Fluid feeding.
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