Are Ants harmful to plants?

[Traceyash]

Im asking this as down here in Surrey,the soil is basically extremely sandy everywhere and when i say we have thousands of ants in the gardens,i mean it,lol. Now i have alot of beautiful flowers in both front and back garden,one of which is in a flower bed out the front which is crawling with Ants but they havent eaten any of the plant. But on the other hand,my precious Rose bushes in the back garden seem to be crawling with them too and they look eaten. Could it be green fly that is eating my plants (leaves),especially clustered around any new buds,and that the ants i see are eating the green fly?

[Grannydrums]

Sounds like the ones on the roses are farmer ants.. They keep greenfly down in there nests and then carry them up to the plants to feed.. Thegreenfly eat your plants and the ant milk the greenfly. I have them and I am thinking of killing the ants. I wonder of the ants kill ladybird lave cos I never see ladybirds on the plants the ants are farming