Yes. Some ants "milk" nectar out of the aphids for the ants' nutrition. Ants protect the aphids from some predators.Have I been watching ants protecting aphids?
I've been watching these guys on the end of a pine tree branch for about 2 weeks now. First, I thought the ants were eating the smaller insects, but they are not. Then, I thought I was looking at an ant nursery, but no. I think I have finally figured out that what I've been watching is ants "herding" aphids in order to consume their nectar. Animal mutualism - the ants get the nectar, the aphids get protection.
I hope someone can confirm that I am understanding this animal interaction correctly.
Ants and Aphids « NORTHWEST WILDLIFE ONLINE
One way I know aphids are on my plants is if there are a lot of ants.