Ants in my pants

The other day I was watching ants go up and down trees. It's become a thing.

So, what i think is happening is that there is a sugar source high up in the tree. It could be tree exudates, apparently, but maybe too they could be feeding on the honeydew of aphids?

When I got home, I went into the garden and whistled. The first time I did that, Juvenile Blackbird showed up; the second time it was Mrs B.; this time it was Son of Bob. I gave him a suet pellet then watched him jump and peck something from the tree stem next to him. An ant. Ants going up and down my cherry - which, I happen to know, has an impressive collection of aphids in the higher leaves.

Mind you, if the aphids pierce the leaves, the tree may exude and maybe the ants eat that?

In the meantime, something is chewing through the leaves of my only-just-recovering-from-pollarding lilac like the hungry bloody caterpillar. Wish the ants - or Son of Bob - would intervene.