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Hematophagia: Vampires are Real!

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.

Common Vampire Bat (Desmodus Rotundus)

There is nothing supernatural about vampire bats, they are simply an animal adapted to a specific diet. Photo Credits.

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.

Anopheles stephensi

This mosquito (Anopheles stephensi) is feeding on human blood by piercing her mouth-parts through the host’s skin. She is digesting the rich nutrients and expelling the excess liquid. Photo Credits.

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.

Vampire Bats (Desmondus rotundus)

These common vampire bats (Desmodus rotundus) are being given a free meal of fresh blood, but in the wild they specialise in stealing blood from sleeping mammals. Photo Credits.

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.

Yellow-billed Oxpecker (Buphagus africanus)

The yellow-billed oxpecker (Buphagus africanus) is one of the two species of African bird that feed on mammals’ parasites. Recent studies have shown they might cause more harm than good by keeping wounds open to drink blood. Photo Credits.

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.

Much love,

-Nick

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Coprophagia: Poop is Food

In previous posts I’ve talked about some of the strange things that animals eat; Geophagia is the eating of soil and rocks, and Osteophagia is the eating of bone matter. For today’s post, I’ve saved the best for last: Coprophagia.

Coprophagia can, basically, be defined as the eating of faecal matter (that’s poo to you and me). It is an unusual and perhaps shocking feeding behaviour to us humans, but many animals practice it regularly and I’ll outline some of the interesting reasons why they do this.

So why eat poo? It seems like a strange question, but the answer is reasonably simple; the digestive systems of animals are never 100% effective and as such, their droppings almost always contain nutrients that have not been digested and used. Let’s take for example an adult African elephant (Loxodonta africana), it can only metabolise about 40% of the nutrients from the food it eats as it passes through its system so quickly. Unused nutrients (along with other waste materials) end up simply being dropped on the ground where they will decompose as a result of the action of fungi and bacteria; but before decomposition takes place, there is an opportunity for animals to make the most of the material and recycle it.

An elephant dung pile broken apart by an army of busy dung beetles.

A dung pile broken apart by an army of busy dung beetles.

As you can see from the picture above (as seen in a previous ‘Photo Previews’ post), dung beetles (from the superfamily Scarabaeoidea) gather in great numbers on dung heaps; they feed almost exclusively on mammal faeces, indeed, they love dung so much we named them for it. Within minutes of a mammal dropping its dung on the ground, dozens of dung beetles will find it and get to work; they burrow through the heap and mould balls of dung into which they can lay eggs, so that later their young will develop inside a ball of food. A solid ‘log-like’ pile of rhino dung can be broken open and spread about by dung beetles in a very short amount of time. We will talk more about the various fascinating behaviours of dung beetles in a later post.

Lagomorphs (order Lagomorpha) are a group of animals that includes rabbits and hares and these animals use coprophagia as a natural part of their digestive process; they have short digestive tracts and are unable to metabolise all of the nutrients they need from their food with only one transit of that tract. After passing food through their bodies once, they eat pellets straight from their anus and send them through again. Thankfully this is a process from which humans are spared.

Scrub hares (Lepus saxatilis) is an example of a lagomorph.

Scrub hares (Lepus saxatilis) is an example of an African lagomorph.
Photo Credits.

Many animals that practice coprophagia do not feed exclusively on faeces; they supplement their diets with nutrients they recycle from animal droppings because they do not have access to the food sources of those nutrients directly. I talked briefly about one example of this in the Osteophagia post; the leopard tortoise (Stigmochelys pardalis) has been observed feeding upon hyena droppings, this is because they contain calcium and phosphorus, nutrients that the tortoise needs but cannot acquire itself. Hyenas are predators and scavengers that are able to crush through bones with their strong jaws and digest it with their powerful digestive systems, but of course, there are always waste products. The tortoise is simply not equipped to crunch through animal bones but has evolved an equally useful strategy to gain the nutrients it needs.

Sometimes animals might feed on faeces but not for the actual material of the faeces itself. Infant white rhinos (Ceratotherium simum) will eat the dung of their mothers because at birth, their digestive systems do not contain the bacterial cultures that help them digest the fibrous grass material that they will feed upon for the rest of their lives, however, their mothers’ digestive system does contain this bacteria and they pass some of it out in their dung. After several months a white rhino calf will have ingested enough of this ‘good bacteria’ that they will be prepared to graze and digest grass after weaning off of their mother’s milk. So as you see, the calf is only eating faeces for the microorganisms it contains, not the partly digested grass.

Awhite rhino baby (Ceratotherium simum) with mother. Calf acquires digestive microflora from its mother's dung before it can graze

A white rhino calf acquires digestitive microflora from its mother’s dung before it can graze.
Photo Credits.

Coprophagia is basically repulsive and wrong to us humans, largely for social/cultural reasons, but it has its origins in the fact that our faeces is mostly toxic to us and doesn’t provide any nutritional benefits. Coprophagia can also be a negative process for other animals too; many animals in captivity will eat their faeces if under stress as demonstrated quite tragically by chimpanzees (Pan troglodytes) in zoos where their complex cognitive, social and emotional needs are not being met.

Hopefully you have been able to see past the ‘grossness’ of coprophagia and still enjoyed reading about it. The natural world is full of fascinating subjects even if it’s not all pretty.

Much love,

-Nick

 

If you liked this entry, make sure you check out our Diet category.
Other Diet entries:
Geophagia: Eat dirt!
Osteophagia: An unusual eating habit that actually isn’t very unusual.
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Geophagia: Eat dirt!

We’ve talked in a previous post about osteophagia (the eating of bones) but this seemingly unusual eating habit is not the only one worth mentioning. Today we can look at ‘geophagia’ which is the behaviour of eating raw materials from the Earth; this might include rocks and soil and so forth; not a very delicious concept I’m sure you’ll agree, but it does serve a variety of useful purposes.

In perhaps its simplest form, geophagia might involve simply eating the soil and a wide range of different species, over 200 in fact, have been observed doing just that. Humans too have been known to dine on some soil from time to time, especially in times of famine, or sickness. But why eat soil? The answer is simple enough; many types of soil contain minerals that can be digested and metabolised by animals; the same minerals that can be found in food sources, minerals such as iron, sodium, calcium etc. When conditions are poor, animals might supplement their diet by practicing geophagia to gain those minerals that they are not currently receiving enough of from their food.

Elephants have commonly been observed practicing geophagia by, most often, eating clay like soils; especially those found at the bottom of water sources. It is believed that they eat these clays because they are rich in salts which provides them with sodium; an important nutritional mineral. Elephants may sometimes be seen digging through sediment with their trunk, looking for the salty clay that they need.

African elephants (Loxodonta africana) crossing a river, drinking water and digging for salty clay along the way.

African elephants (Loxodonta africana) crossing a river, drinking water and digging for salty clay along the way.

Many birds practice geophagia, but not necessarily for nutritional reasons, but still to aid in digestion. Birds have a specialised organ in their digestive tract called a gizzard which is used in the grinding up of food stuffs (birds do not have the luxury of chewing as they don’t have teeth). The gizzard is composed of strong muscular tissue that  crushes and grinds food to allow for more effective chemical digestion, but many birds enhance their gizzard’s effectiveness by swallowing small stones or grit that stay in the organ, breaking down food particles, these pieces of stone are referred to as gastroliths.

Ostriches (Struthio camelus) can carry gastroliths as big as 10cm.

Ostriches (Struthio camelus) can carry gastroliths as big as 10cm.

Crocodiles, which are surprisingly close relatives of birds, also consume gastroliths, but not just to help in the grinding up of food for easy digestion; by holding rocks inside their bodies these aquatic reptiles are able to affect their buoyancy in water and more effectively control their ability to float or sink as needed for temperature control or for ambushing prey.

So it seems that although geophagia might appear to be an unappetising prospect at first, it actually has useful purposes; in fact, many animals would not be able to survive without it. We humans can even give it a go too (not that WildlifeTV recommends it!) in certain cases.

Much love,

-Nick
 

 

 

If you liked this entry, make sure you check out our Diet category.
Previous Diet entries:
Coprophagia: Poop is Food
Osteophagia: An unusual eating habit that actually isn’t very unusual.
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