You might think that, considering its fame, the chupacabra is a beast of ancient legend. In reality the first word about chupacabra appeared in 1995*, when eight sheep were found dead in Puerto Rico, drained of blood. Later that year a woman named Madelyne Tolentino saw the creature responsible; her description would become the basis for the chupacabra. But what did Tolentino see that night? What was it that became the source of the legend?
Assuming we don't believe that the chupacabra is a real thing, investigator Benjamin Radford has a theory: the chupacabra is Sil from the movie Species.
Let's take it a step back, to the night that Tolentino saw the monster. Here, paraphrased by Radford, is her description:
Tolentino said the chupacabra she saw had dark eyes that went up its temples and spread around the sides; it was about four feet tall, walked like a human on two legs, and had thin arms and legs, with three fingers and toes at the end of each limb. It had no ears or nose, but instead two small airholes. She also noted a row of distinctive spikes on the creature’s back. It stood outside a window, then moved into the road and leaped off into tall grass in a neighbouring vacant lot.
Here's the famous illustration made from her description:
He goes on to note that her behavior at the sighting was... weird. She joked that the monster was missing an asshole, which is a pretty strange detail to notice when viewing a bizarre and unique and predatory lifeform.
Radford, writing in the unmissable magazine Fortean Times last year (yeah, it's old but I'm clearing out my bookmarks here), notes that Sil, created by HR Giger, is a perfect match for Tolentino's chupacabra, all the way down to details of behavior, like hissing and leaping about. Radford notes no less than a dozen morphological similarities between the fictional monster and Puerto Rico's supposedly real terror. But of course that isn't enough to truly claim that Tolentino's famous sighting is based on a movie monster. You would have to prove that she saw Species before she saw the chupacabra.
It turns out she totally did.
As it happens, Tolentino is on record as saying she did see the film before her chupacabra sighting. She told me this herself in a 2010 interview, and the claim also appears in an interview reprinted as chapter five in Scott Corrales’s book Chupacabras And Other Mysteries. Tolentino states that she saw “a movie called Species. It would be a very good idea if you saw it. The movie begins here in Puerto Rico, at the Arecibo observatory. [The monster] made my hair stand on end. It was a creature that looked like the chupacabra, with spines on its back and all… The resemblance to the chupacabra was really impressive.” Later in the interview Tolentino says, “I watched the movie and wondered, ‘My God! How can they make a movie like that, when these things are happening in Puerto Rico?’” She is then asked, “In other words, does [Species] make you think there might have been an experiment in which a being escaped and is now at large? [in Puerto Rico].” Tolentino responded: “Yes.”
There are some nits to be picked. Species hit theaters in the US on July 7th, 1995, about a month before Tolentino's sighting. Was Species released in Puerto Rico at the same time as it was in the mainland United States? I can't find that exact information, but a look at current Puerto Rican movie show times indicates that Puerto Rico is getting pretty much what we're getting - Contraband and Beauty and the Beast 3D are playing right now. That could have been different in 1995, but even if so does that matter? Couldn't Tolentino have simply seen a bootleg of the film? Even before rampant internet piracy it was fairly easy to get your hands on new movies on VHS back in the day.
Of course she could be confused (or been questioned incorrectly) and didn't see Species until AFTER her chupacabra sighting, but this does seem the most likely explanation for what she saw - and what became the leading (but not only) visualization of the goat sucker.
* Researchers point to earlier cases of livestock desanguination in Puerto Rico; at the time they were blamed on the usual suspects, ie Satanic cults.