This must surely be "Eripmav", a (very) short story by Damon Knight, first published in the Magazine of Science and Science Fiction in June 1958.
As the OP recalls it deals with Earth colonising a planet in the Fomalhaut system called "Veegl":
The Veeglians, like all higher life on this world, are plants; the Veeglian vampire, needless to say, is a sapsucker
A Veeglian girl is found complaining of lassitude, and two puncture wounds are found in her neck. The Earthmen find and kill the Veeglian vampire responsible, and the story ends:
Afterward he seemed dead enough, but the local wiseheads advised us to take certain precautions. So we buried him with a steak through his heart.