Apparently, aphids eat plant sap, and then for some reason secrete a sticky fluid known as honeydew.
Ants like sticky.
And then I'm told, a black sooty mould follows.
That sounds a lot like what I'm seeing on my strawberries.
Here is a picture of an ant licking some PVC and enjoying some sticky.
120 things in 20 years - not just Aquaponics - Honeydew