Excellent question, I have some star polyps growing next to a colony of zoas and for the better half of six months they form a type of no-mans land between them, even though it is a small line between the two. The blue zoas will not grow next to the star polyps and the star polyps have not grown toward them. If yours do grow over your zoas, it can be easy to remedy since they form a mat and can be pulled off. I have not noticed any stinging when they touch.