Omalus aeneus is a species of cuckoo wasps belonging to the family Chrysididae.

[1] Subspecies include:[2] This species is present in Europe (Finland, Germany, Italy[3] and Switzerland), in the East Palaearctic realm including China, Taiwan and Japan, in the Near East and North Africa, and in the Nearctic realm.

The body color of these small wasps is blue, green, purple, sometimes almost black or golden, the abdomen and legs are greenish-blue, the tarsi are brown.

[5][7] Similarly to Omalus biaccinctus, this species has also been reported laying eggs inside living aphids, later preyed by aphid-hunting crabronids.

In such a way O. aeneus through the aphids can enter in the nest of the crabronid in order to lay its eggs.