Aphids on the tip of purple foxglove, being attended by ants, which harvest the honeydew being secreted from the aphids. In the upper part of the image, a parasita wasp is visible (cf. upper image note). In the lower part, a few already parasitized dead aphids (brown and expanded) are visible (cf. lower image note).
In higher magnification, a parasitic wasp is well visible (cf. image note; the wings of wasp are oriented parallel to the wasp's body while the wings of winged aphids are standing upright.) The wasp injects an egg into the aphids and the larvae grow in the aphids, which finally causes some expansion of the aphids. Several aphids on the photo appear expanded and brown instead of black, indicating that they have already been parasitized.
Stem of a purple foxglove with living aphid colony and ants. Based on the wing orientation there seem to be several parasitic wasps on the colony (cf. image notes). These parasitic wasps can lay eggs in aphids undisturbed by the ants, because they have a chemical camouflage such that the ants think that the wasps are either other ants or are aphids.
Stem of a purple foxglove with dead aphid colony. The larvae grow inside the aphids, they eat from the inside out completely and then cut a round hole in the aphid, through which they finally leave the host. The ants are all gone because there is no more honeydew to collect.