You know how people buy boxes of ladybugs to release in their yard to get rid of aphids
Picture this: slew of missing people from all over the world, just vanishing in small groups. Serial killer ring, some say. Some kind of widespread natural disaster, say others. The statisticians shrug and point out that people go missing all the time and one expects peaks and troughs in random data. Sometimes a lot of people are going to go missing and it doesn't necessarily mean anything weird.
Everyone turns out to be wrong. It's alien abductions. Aliens are coming to Earth, pinking up random groups of humans and not bringing them back.
Turns out aliens are trying to settle a new planet and there's a problem with a bunch of prey animals breeding out of control and upsetting the ecosystem. They can't wipe them out wide scale without destroying complex environments, and the predators aren't keeping on top of them. "Hey," says some random bureaucrat who's had Project: Deal With The Alien Deer Issue dumped on their desk and hasn't taken an ecology class in four decades, "you know what species I hear are really, really good at clearing other animals out of the environment?"