Is gross. There are so many pleasant things to eat and they wanna munch butt..... I have heard that related to a parasitic host take over for mating, kind of like that one that makes the snails get ate by the birds and I am at a loss. Maybe you are correct, I am just so not able to accept "aliens". Not from space. How those little critters fly all the way over here. They got little space suits and space ships. Little pew pew lasers? Could easily be an altered existing species meant to do what they do. They were doing some strange shit with animals in the distant past and they are doing it again.