[al78]

Is this anything to be concerned about, or should I just treat it as part of the local ecosystem and leave it alone?

[Beetroot queen]

Isn't it a sign that the heap is too dry, you can give it a good dig and they move on I think. Lots of ants about down here. I think they can also be left to get on with it but it's personal preference

[compostqueen]

They do say that ants harvest aphids so that's a good thing. I've had them in mine very often and I don't mind them at all.  It's all part of the lifecycle of the bin