Where do Mr. and Mrs. Worm come from, then?
If you start out from scratch, with no worms, still you soon get millions of worms from who-knows-where.
Our compost bins invite mice and ants to nest.
This seems not to be a problem though.
The ripe compost gets shovelled out from the bottom, and everything sinks down, while the centrally-heated colonies of mice and ants migrate upwards to the surface. They seem to actually assist the process. Maybe roaches do the same, but being roaches, we don't like them to be there.