Hematophagy is when an animal feeds on blood. It's usually one of the first things that comes to mind when bats are mentioned. And yet, it isn't just something creepy that our furry friends do, but is quite common in the animal kingdom (even people eat foods that contain blood).

First off, I think it's important to say that only 3 types of bat out of the 1,100 known species are hematophages (blood feeders). It's common among insects, worms and perhaps more unusually, there's even a type of fish called the lamprey that has a blood diet.

If you're like me, you might be wondering why any creature would feed on blood. The truth is that it contains all the nutrients an animal needs for survival. Proteins, carbohydrates in the from of glucose, fat and minerals like iron.

And despite the risk of being swatted or crushed, feeding on another organism's blood can be an easy way to get a meal.

Stealth and silence are needed in order to be a successful hematophage. Animals like vampire bats have evolved some pretty nifty adaptations that enable them to have this sort of diet.

They've got very sharp teeth which are used to shave a host animal's hair and to penetrate its skin easily. Like other blood feeders, they've also got a whole suite of chemicals in their saliva which makes obtaining their meals easier.

Anticoagulants to stop the blood from clotting, vassodilators to prevent the blood vessel from closing, anti-inflammation substances and even anaesthetics to make sure the host doesn't feel pain.

It'd be nice to think that the anaesthetic substances are there out of consideration for their hosts but it's probably more to do with reducing the risk of discovery.

Hematophagy is a bit of mixed bag as far as it's effects on other animals go.

On the plus side, it's provided quite a few medical benefits for humans. Draculin is an anticoagulant found in (you've guessed it) vampire bat saliva and is one of the most powerful ones known to humankind.

And hirudin, which is found in leech saliva is another potent anticoagulant.

One of the down sides to hematophagy is that there's the risk of disease transmission from feeder to host. Illnesses like sleeping sickness, rabies and malaria are just a few of the ones that can be passed on.

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