O. aeneus [1,2] is an uncommon wasp that occurs in the middle and South of the Netherlands [3,4].
The species is active from May up into August .
O. aeneus hunts for small digger wasps of the genera Passaloecus and
- Passaloecus turionum
- Passaloecu gracilis
- Passaloecus eremita
The male and female are 3 – 7 mm  in length.
The characteristics of the species are [2,3]:
1. Female is entirely deep blue, violet or green
2. Male is dorsally black, with blue or green reflections on the side.
3. Base radial vein frontwing curved
4. Medial veins frontwing slightly curved, ie. has an angle larger then 90° (a strongly curved vein makes an angle of about 90°)
5. Head and mesosoma with short hairs (not visible in photos)
6. Temples angular when seen from above
7. Fine punctuation on mesoscutum
8. Sparser and finepunctuation op pronotum (sometimes coarser)
7. Metascutellum not elevated
8. Side thorax, mesopleuron, weakly projecting
9. Margins of mesopleuron tip shape an obtuse angle
10. Margin of abdomen without enlargement or thickening, rounded and relatively straight
11. Shallow notch on tip tergite III (not visible on photo)
12. Tergite III without teeth and pit row
4. PARASITIC RELATIONS
The following hosts of O. aeneus are present in the garden:
- Passaloecus gracilis [2,3]