Vampires exist, but they are not in human form as legend has it. The Earth has evolved creatures, mammals, that bite and drink blood - the vampire bats that plague certain tropical countries and debilitate range cattle with blood loss. Are Vampire bats the basis of the Vampire legends? In a manner of speaking, as the legend is based on a similar creature that evolved on another world. Just as Dragons were brought to the Earth by aliens in the Service-to-Self orientation, to terrify humans they hoped to later recruit into their ranks, just so were large Vampire bats brought to Earth.
Then why the legend of the bat becoming human? The visitations occurred at night, as these bats evolved in a similar manner to the Earth's bats, using squeaking sounds in a type of radar, and using the safety of darkness to escape predatory birds which consider rodents a full course meal. The imported bats were large though slender. When flying they looked like bats, but after they landed their folding wings looked like outstretched arms - the vampire in his black cape. Red eyes? Yes, indeed in any light nearby the eyes, which lacked the protective pigment necessary in harsh daylight, showed only the blood just under the surface of the eye. And just as some hairy monkeys on Earth have hairless, pale faces, just so did these large Vampire bats have hairless faces. They were chosen by the Service-to-Self aliens because they resembled humans, in the dusk. The terrified victims, frozen in fear, gave birth to the Vampire myth of supernatural powers.
Were they found and killed with stakes? They were killed with whatever was at hand, when discovered in their dark lairs, and what was mostly at hand were wooden sticks. Farmers staking fence posts would use the pointed ends to fend off attacks from wild animals, and in most cases this was the only weapon available when fending off an attack from Vampires.