"Hi, Colonic" is a short story by Harry Turtledove, first published in I, Alien, edited by Mike Resnick, DAW 2005. It was reprinted in Galaxy's Edge Magazine, Issue 14, in May, 2015.
The story is a humorous look at modern American lore about close encounters with aliens, specifically the common theme of aliens abducting people from the poorer parts of the country (so-called "rednecks" or "hillbillies") and rectally probing them. An unnamed alien explorer and his partner arrive on Earth in search of intelligent life. They take three hunters from an Arkansas swamp and rectally probe them. The aliens find no intelligence in the firsttwo, but they have luck with the third one. Here the story reveals its punchline: the intelligent life they find are hookworms in the third man. The alien explorers are far more evolved relatives of these worms. As a consequence of their biology, they don't perceive humans as being intelligent.
Having made contact with the parasites, the alien explorers return the humans to Earth, and bemoan the fact that they will now have several reports to file. A brief coda shifts back to the three hunters, who suddenly find themselves standing around with their pants down, and no memory of how it has happened. The one with the worms seems to realize he is "not alone" and that is it is not a good thing.