L. niger have queens in the beginning but then dominate kills the weaker one when workers develop., or the workers kill the weaker queen I forget.
That is true (also for Lasius flavus ) the queens will fight and if you are lucky the strongest one will survive, is she is not hurt to bad.
Not many species can live together (some can), you can not do this like in nature, in nature they will avoid each other but in captivity they have not much space and they will fight for food and room.
how would a colony of lasius flavus get on with L. Niger?
The weather has been poor all week here so i still havent been over to my nans...
Depending on the weather i may go tomorrow....So ill let you all know
if they have enough room and enough food there will not be many problems but Lasius niger are very aggressive against other ants if they come to close (you would not say because of there size, but they are ;) )
Really? I would have thought that L. Flavus were the more aggressive?
Not in my experience. ;)