Thanks for that great info...
 

I have not seen any real bad damage, but I only noticed them 2 weeks ago and have been away for 6 days and will see them again tonight for the first time since my mini-vacation.

It is true that they so match the birds nest so that you can barely notice them when they are active, so could have been there for months - from where, I know not.

if it were me, I would just take pleasure in such a unique symbiosis occuring in my tank and just enjoy them until you notice any detrimental activity.