Since blood is a fluid tissue rich in nutritious proteins and lipids that can be taken without great effort, it looks like hematophage animals would be above carnivores in the food chain.
Animal tissue (meat) has much higher energy content than plants but still needs to be broken down in proteins. Breaking down those protein through digestion costs some energy.
Blood already contains those broken down nutrients and it would seem that it s even more energy efficient than meat.
On our planet, only small animals are hematophage. I wonder if it s because it would be too difficult for a larger animal to constantly hunt bigger animals and drink their blood.
Therefore I m wondering if a human sized animal could entirely be hematophage.
Also would it be possible to modify our DNA to make our digestive system be able to digest blood? That would turn us into vampires!