Do ants eat aphids?
Ants all over your plants?
You may think they are there to eat the invasion of aphids (greenfly or blackfly) you have had but they are actually attracted by the honeydew the aphids produce when feeding. Ants don't eat aphids.
Ants protect aphids
Ants (quite brutally) ward off natural predators of aphids. If an aphid eater like a ladybird or lacewing tries to eat the aphids then the ants will mobiles to remove them. Ants will lift off or crush the aphid predators before they have a chance to feed on the aphids so that the ants do not loose their food source.
How to get rid of aphids when ants are present
Ideally you would control the ants first. We sell a type of nematode that you treat ant nests with. It doesn't kill the ants but it moves they away from that nest. You can also remove the ants physically with a blast of the hose. Blasting the hose will remove some of the aphids too.
Using a product like horticultural soap to reduce the aphid population will cause the ants to leave the plants too, as their food source (the honeydew) will no long be being produced.
Aphid Predators that fair well against ants
The wasps and midge that we sell for aphid control work well when you have lots of ants. This is because they act quickly and to not spend lots of time on the plants. More on all the aphid predators and controls here.