Define filth. What we call spoiled food is great for basically all the critters entering our houses. That’s where the stigma comes from - if you don’t really clean your kitchen and leave scraps and crumbs in narrow spaces, that’s where they will feast.

While I’ve yet to see cockroaches in the wild in Germany, ants inside the house can be prevented by just cleaning regularly (and not even obsessively).

It’s not like lice for example, that really don’t care how often you wash yourself and infect anyone with long enough hair.