It's a Centaurea and i have loads of clumps here and mine too are covered in ants if i don't spray them.
No idea though why they're so attracted to them !

I wasn't aware of them being part of the Geum family so can't comment on that.

Thank you Louise..i wasnt sure about the Geum connection..what do you spray it with?

Not even remotely related to each other. Geum is related to Roses of all things and Centaurea is related to Daisies.
Never seen ants on our Centaurea, but there must be something on the buds they like, either greenfly which they farm or some sort of sugar exuded by the plant itself.

Yes, they must be good hosts, Owdboggy !

Skipscanda, i spray with an insecticide called Provado.
These plants are regularly troubled by ants and i only spray about once a month as the ants don't bother me being on the plant - i just don't want to encourage more ants than i already have here !

I also have this plant - Centaurea. I don't spray it at all, and it doesn't seem troubled by anything. I have C. montana.