My parents have a cabin in the countryside near fields and at some periods of the years there's hundreds of them inside, crawling on the windows. You end up squishing some involuntarily, just walking around.

They vacuum them outside but it's kind of useless as they just come back.

EDIT: The windows facing the sun just look like this

They get everywhere. Recently we opened some walls and there's just ladybug carcasses everywhere. Removing a wall trim? Ladybugs behind it. Changing a light fixture? Dead ladybugs everywhere in the ceiling. Most of the cabin must be constituted of ladybug cadavers.