Chewed petals apparently secrete a sugary liquid that some ants would want to collect. The ants might do the chewing or may discover it. There are a million different ant species, all with different behavior. I have seen ants on rosebuds that had been cropped flat. I sprayed the basal canes with insecticide and they went away.

Can't really tell anything from that picture.

Ants don't "eat" rose petals. As Michael said, something else chewed up the petals, releasing sap which is sugary. The ants eat that sugar, just as they eat the honey dew from aphids and other sucking insects. Figure out what chewed up the bloom, deal with it and you should prevent the ants from being attracted to the blooms.

I always had that issue with the green roses (Greensleeves, Mint Julep, Sheila MacQueen, etc.) as the petals were heaven for aphids. They would provide their honey dew after sucking out the sap from the petals and the flowers would be full of ants. I dealt with the aphids and the flowers were ant free. Kim

I better try to get a better photo. I keep on thinking thrips. I used to have absolutely TONS of aphids on my roses,but the blooms seemed fine. Then,these nasty Oxythyrea funesta beetles invaded. In hopes to get rid of them, I started spraying a systemic insecticide,Confidor.It did nothing to stop the beetles(if anything, made them stronger!) but got rid of the aphids completely. Now, I have all these crummy looking blooms on some of my light coloured roses. I've completely stopped spraying insecticide; I've gotten the impression that my roses began to look worse once I started spraying. But I could see using a systemic via irrigation on specific plants,if it would be effective against the specific scoundrel that's doing the damage.
I will try for a better photo,but it may have to wait for next year at this point; my rose season is basically over. regards and thanks, bart