Animals eat all sorts of things. The diversity of species in the animal kingdom is matched by the diversity of diets. In previous posts we’ve seen how some animals will eat bones (osteophagia), rocks or soil (geophagia), and even faeces (coprophagia). The next ‘phagia‘ we’re going to look at is hematophagia; feeding on blood.
When we think of feeding on blood, the animals that come to mind are blood sucking leeches and pesky mosquitoes but in reality, it is a widespread feeding behaviour utilised by a broad range of species. There are two categories of animal that feed on blood, obligatory and optional; some animals exclusively feed on blood (they are obliged) and some just supplement blood into their regular diet (it is an option). We call animals that feed on blood ‘sanguivores‘
So why does blood make a good meal? Blood carries vital chemicals around the bodies of many animals and as is loaded with nutrients, proteins, salts and fats; it is a nutritious and high energy food source. Most predators, such as big cats, will gain the nutrients found in blood because they eat all of an animal’s tissues, but hematophagy is used to describe when animals specialise in feeding on this valuable food resource.
Blood is, of course, kept inside animals’ bodies, so in order to drink it, a certain amount of ‘surgery‘ is required. The process of accessing blood is called phlebotomy, it involves cutting into flesh and revealing veins, arteries or capillaries. The tools used by hematophagic animals are almost always their mouth-parts but there are many different anatomical approaches.
The first part of phlebotomy is cutting the flesh; mosquitoes (family: Culicidae), ticks (superfamily: Ixodoidea) and other blood sucking invertebrates have sharp mouth-parts that pierce the skin and dig down to find a source of blood, they then suck up the liquid or let the victim’s blood pressure force the blood into the diner’s mouth. Vampire bats (subfamily: Desmodontinae), found in Central and South America, have a slightly more crude and messier method, they simply use their teeth to slice open their victim’s skin and then lap up the pool of blood that comes out of the wound with their tongue. Interestingly, vampire bats will also use their teeth to trim fur away from the site where they intend to feed.
So vampires are real, but they aren’t supernatural beings, they are animals looking for a good meal, and there are many different species.
Vampire bats are a special group of bats that have become specialist blood drinkers, hence their name. They do not rely on echolocation like many other bats but instead they have specialised senses for finding sleeping mammals on which they can feed. They sniff out carbon dioxide (CO2) and chemicals found in sweat, and have special thermoreceptors on their noses which allow them to detect heat; this also allows them to find warm spots on an animal’s body where blood is closest to the surface.
Mosquitoes are perhaps the most famous blood suckers, however, in reality they are not exclusively hematophagic. Not all species of mosquito feed on blood, and for those that do, it is only the females. This family of flies has evolved to feed on nectar and fruit juices but the females of some species have adapted their mouth parts and specialise in drinking blood from the bodies of mammals or birds. But why only the females? The reason for that is related to the nutritiousness of blood as a food source; they use the extra nutrients to help in egg production and development.
Sanguivorous animals are generally parasites; they take blood from their hosts and give nothing back in return (except maybe for a nasty disease). There is one animal that until very recently was thought to be beneficial to it’s hosts, but the relationship is not what it seems. Oxpeckers (genus: Buphagus) are Southern African birds that spend their time riding large grazing animals around, feeding (mostly) on ectoparasites such as ticks. A large animal like a giraffe (Giraffa camelopardalis) has a lot of surface area and a lot of blood and as such attracts a lot of parasites. Oxpeckers have found that riding along on a giraffe is a great way to find all the food they need. It used to be assumed that oxpeckers provided a wonderful service to the large mammals of Africa but recent studies have shown this might not be the case. Although oxpeckers are very fond of ticks (which are already full of blood), they also practice hematophagia and will regularly drink fresh blood from wounds on their host mammal’s body. Oxpeckers will even open up wounds and prevent them from healing so that they have a regular source of blood, this can be painful for the animal as well as putting them at risk of infections.
Hematophagy in practice can be a risky business; anyone who has been bitten by mosquito knows that their first response is usually of aggression and the same is true for other animals. Feeding on an animal’s blood requires physical contact and if caught, there is a possibility of being attacked or even killed. However, blood is such a valuable food resource that many animals are willing to take on these risks in order to obtain it, and many of them have a few tricks that help them get away with it.
Most blood drinking animals have special saliva that delivers a cocktail of chemicals into the bite site when they start to take blood. Their saliva can contain anaesthetics that prevent the host from feeling the bite and reacting to it, and also anticoagulants which prevent the blood from clotting so that it stays liquid and drinkable.
Animals have formed complex relationships with one another when it comes to feeding. When we think of animals feeding on other animals we tend to imagine large predators killing and devouring their prey, but in reality, some species have developed techniques for getting the sustenance they need without so much theatrics.