Many aphid species provide ants with honeydew and ants in turn provide aphids with protection: a mutualistic interaction. A gall aphid, Paracletus cimiciformis follows this paradigm but also has interctions not beneficial to ants. The primary host of the aphid is the tree Pistacia terebinthus. The aphid makes leaf galls. Winged aphids emerge from the galls and colonize grasses. Paracletus cimiciformis has two morphs that feed on the roots and produce honeydew, a round and a flat morph. Both may be visited by ants in the genus Tetramorium. The round morphs produce honeydew rewards and remain on the plants. The flat morphs are chemical mimics of ant larvae. The ants mistake the flat morphs for ant larvae and carry them back to the brood chamber with the developing ant immatures. Once in the brood chamber, the flat morph aphids feed parasitically on the hemolymph of the ants.
I am surprised to learn that some aphids can be predators. However, insects are opportunistic and given the availability of a resource, some insect is likely to find a way to exploit it.
Adrián Salazara, Benjamin Fürstenaub, Carmen Queroc, Nicolás Pérez-Hidalgod, Pau Carazoa,e, Enrique Fonta, and David Martínez-Torres. 2015. Aggressive mimicry coexists with mutualism in an aphid. PNAS. 112: 1101–1106.