A black garden ant (Lasius niger) farms White-banded Dogwood Aphids (Anoecia cornicola) for sweet honeydew.
The ant 'milks' the aphids by stroking them with its antennae, encouraging the aphids to produce the honeydew. In return the ant will protect the aphids from predators such as ladybirds. Sometimes the ants will pick up aphids and move them to another part of the plant, or a new plant to start a new colony or 'farm'.
The White-banded Dogwood Aphid (Anoecia cornicola) is an aphid that feeds on Dogwood (Cornus), the ones in this image they are feeding on Cornus alba. The winged form of Anoecia cornicola has a white band around the top of the abdomen, and a prominent black spot at the end of the principal veins. The cornicles in Anoecia cornicola are merely pores.
The black garden ant (Lasius niger) is the most common ant seen in Britain. The worker ants, which are the ones you will normally see (and shown here) are non-reproductive females. They are dark brown, covered in small hairs, and around 3-5mm long.
Cropped in ACR