Since we do not know what "visitors" we might have had from another galaxy over the thousands of years that man has lived here on the earth; I think we would be reimiss if we didn't also conside the possibility of what we call a vampire coming from somewhere besides our planet.
We have some very unexplainable things that happen here, and they are also blamed on aliens from spaceships.
Consider, first of all, the cattle mutilations. We don't hear of those as often as we used to; but I think it is just that it is no longer an mindblowing story when someone reports.
These cows are not just chopped up cows. There is a pattern to what happens to these cattle, and it is always a similar thing, regardless as to where on the earth the mutilation takes place.
The animal is often found in a burned-looking circle, and there is no blood like there would be if this were simply an attack by wild animals or even by cattle thieves.
Another mostly unexplained thing are the strange circles found uually in large fields, and called "crop circles. Though some of these have been proved to be a hoax, there are many that are still a mystery.
These are only part of the strange and unexplainable things that happen , and it seems to me that some sort of a vampire alien is also possible.
http://www.aliens-everything-you-want-to-know.com/CattleMutilations.html