Once, scary monster movies were all about giants. The fifties had giant ants, giant spiders, and the occasional giant octopus. Then something changed: We still get giant monsters, but modern films know that small is scarier than big.
Do you know what I'm scared of? Killer dogs. Do you know what I know is not in my room right now? A killer dog. The room is just not that big, and it has a lot of open space.
Do you know what else I'm scared of? Spiders. Do you know what is in my room right now? A spider. I could just be playing the odds in telling you this, but I'm not. I saw one on the ceiling, where I couldn't get to it, and when I came back in with a chair it was gone. It's somewhere in here. I just can't see it.
That's one of the many, many reasons small scares are worse than big ones. Big monsters rely on power, on being extraordinarily huge and vicious. Small creatures are already part of your everyday life. A movie about a big creature has to establish how powerful it is, how it can get from place to place, how it can manage to hide and suddenly pop out of nowhere when you thought you were safe. Small critter movies don't have to do any of that. They just have to rely on what you already know. Small things can already find their way into you safe spaces. Everyone has tried to patch up all the small holes in their house, has tried to seal up their tents, has tried to shake out their clothes and their sheets, only to find the bugs coming back. No one wonders how small creatures get from place to place. They're everywhere. Always. And of course, no one has to wonder how small things hide.
Big is intimidating. Small is unstoppable. Movies don't have to show this. It's already part of your everyday life. Is there anything scarier than that?