Since the second generation was born my ants seem a lot more agitated when I check on them, and move around in a very fast, jerky way when I disturb them. Before the 2nd generation was born they never moved like this, is this aggressive behaviour or something?
Yes it is natural that the first generation of ants are a bit less aggressive when 2nd generation comes they turn a bit more aggressive...
In deed the first generation need to stay alive to start up the hole colony so they are more shy than the second one.