My kids and I encountered a situation where every minion start space was occupied by at least one roach, and then a surge occurred which brought in a spider which is a large minion.

As per my understanding, a space can have either four small minions or one large minion.

So what do you do if all start spaces are occupied by one or more small minions, and then a large minion appears via a surge or other effect? Does the large minion simply not appear, or does it take the place of one of the smaller minions on the start space?

Is it permissible for mice to occupy a minion start space as a strategy to prevent new minions from spawning in there?