During the course of my many Chupacabra investigations on Puerto Rico (from 2004 to 2018), barely a day went by when I didn’t hear at least one story of the chupacabra’s vampire-like attacks on livestock and other animals. And I can’t tell you how many times the words "blood" and "draining" (or "sucking") were used in the very same sentence. Certainly, I uncovered a number of stories from people who claimed their dead animals were subjected to necropsies, and which confirmed that massive blood loss had occurred. The problem, however, was that I was never able to secure even a single, official necropsy report to validate those claims. On the other side of the coin, I have heard more than a few stories suggesting the assumed, huge loss of blood was actually due to the blood of the dead animals sinking to the lowest parts of the victims' bodies, after death. What appeared to have been evidence of a significant loss of blood may, then, have really been be due to nothing more than wild, and uninformed, misidentification. And on the issue of misinterpretation, it’s important to understand the biology and processes involved in those creatures that do dine on blood.
When it comes to the matter of animals that ingest and digest blood (a process called hematophagy), you might be surprised just how many there are. The long list includes bed-bugs, lampreys, Torpedo snails (a type of sea-snail), fleas, horseflies, and Geospiza difficilis septentrionalis – the "vampire finch" of the Galapagos Islands, which happens to be the only known bird on the planet that supplements its diet with fresh blood. Of course, the most famous of all the blood-drinking animals is the bat. More specifically: the vampire bat. There are no less than three kinds of vampire bat: the hairy-legged, the white-winged, and the common vampire bat, all of which have their origins in the New World. Interestingly, and just like the chupacabra, the white-winged vampire has a particular liking of the blood of goats.
Just like its horror-movie counterpart, this particular breed of vampire prefers to spend its time in places dominated by just one thing: darkness. Caverns, tunnels, abandoned buildings, and caves are among the most favorite abodes of the vampire bat. To say that the vampire bat is a unique creature is not an understatement. It uses what are termed thermo-receptors – sensory neurons – to identify those parts of potential prey where the blood is closest to the surface of the skin and easily accessible. In terms of its attacks, and again just like its fictional, horror-movie-based counterparts, the vampire bat very often feeds on creatures that are sleeping, as this makes them far less likely to fight back. The brain of the vampire bat – and primarily the inferior colliculus, which controls how the brain interprets sound – is particularly honed to allow it to detect an animal that is specifically in the sleep-state.
There are other parallels between vampire bats and the likes of the characters in True Blood and The Strain. To survive, they have to keep drinking blood. Studies have shown that vampire bats cannot go for more than approximately forty-eight hours without a significant amount of the red stuff flowing through their systems. Perhaps most fascinating of all is what happens when a vampire bat fails to find fresh blood. It will approach another member of the colony and, in a fashion that is still not fully understood, give a sign that it is in dire need of food. The other bat, in response, will regurgitate tiny amounts of its own, recent intake of blood, thus providing its fellow-vampire with much-needed nourishment. Now, we come to the most important aspect of the life and feeding activities of the vampire bat. If it shatters some cherished assumptions, that’s too damned bad, but – contrary to what many people believe – vampire bats do not suck blood. Ever. Instead, when a bat lands on its sleeping prey, it makes a tiny incision, with its razor-sharp teeth, that provokes the flow of blood – in much the same way that blood flows to the surface of our skin when it’s cut. The bat then proceeds to lap the protein-rich blood, rather than suck it.
That's the truth of the matter. As for the Chupacabra, so far no evidence of specific blood-sucking has ever been found. Only in the domain of friend-of-a-friend-type tales.