CONTENTS

1. Distribution
2. Behaviour
3. Plant relations
4. Prey relations
5. Parasitic relations
6. Identification

1. DISTRIBUTION

Omalus aeneus ^{[Soortenregister]} is an uncommon wasp that occurs in especially the middle and south of the Netherlands ^{[Peeters et al. 2004],[Waarneming.nl]}.

Gardenspecies

The species has been first observed in our garden in 2019.

2. BEHAVIOUR

2.1. ACTIVITY

Omalus aeneus is active from May to August ^{[Peeters et al. 2004]}.

2.2. DEVELOPMENT

Omalus aeneus is generally univoltine, overwintering as larva ^{[Krombein 1967]}, but more than two generations have been observed in Southern Europe ^{[Wei et al. 2014]}.

The species is a Cleptoparasite on smaller Pemphredonidae digger wasps from the genera Passaloecus en Pemphredon en Psenulus ^{[Paukkunen et al. 2015],[Peeters et al. 2004]}. She lays her eggs on potential prey at the host hunting grounds, that will catch and transport to their nests. The cuckoo wasp female therefore does not need to enter her host’s nest, thereby avoiding conflicts and potential injury ^{[Paukkunen et al. 2015],[Winterhagen 2015]}.

The white semi-transperent thinly-walled cocoons are five millimeters in length ^{[Krombein 1967]}. The final instar is described by Tormos ^{[Tormos et al. 1999]}.
The host brood cells may be longer in length at certain nest diameters when parasitised by O. aeneus ^{[Fricke 1992]}.

3. PLANT RELATIONS

3.1. FOOD PLANTS

The following plant species are mentioned in literature as food sources:

Apiaceae [Paukkunen et al. 2015]
Euphorbiaceae [Paukkunen et al. 2015]

4. PREY RELATIONS

Omalus aeneus is a cleptoparasite on several digger wasp genera ^{[Paukkunen et al. 2015],[Peeters et al. 2004]}.

The following species and group occurring in the Netherlands ^{[Soortenregister]} are mentioned in literature:

Spheciformes (Digger wasps)

Pemphredonidae [Morgan 1984] Passaloecus – Pa. corniger [Fardiansah et al. 2024],[Ruchin & Antropov 2019],[Paukkunen et al. 2015],[Peeters et al. 2004],[Blösch 2000],[Strumia 1997],[Woydak 1996] – Pa. eremita [Ruchin & Antropov 2019],[Paukkunen et al. 2015],[Peeters et al. 2004],[Blösch 2000],[Strumia 1997],[Lomholdt 1984],[Lomholdt 1973] – Pa. gracilis [Ruchin & Antropov 2019],[Paukkunen et al. 2015],[Peeters et al. 2004],[Blösch 2000],[Strumia 1997],[Woydak 1996],[Lomholdt 1984] – Pa. insignis [Fardiansah et al. 2024],[Strumia 1997] – Pa. singularis [Ruchin & Antropov 2019],[Paukkunen et al. 2015] Pemphredon [O’Neill & O’Neill 2018] – Pe. lethifer [Ruchin & Antropov 2019],[Paukkunen et al. 2015],[Strumia 1997 (as Pe. lethifera)],[Woydak 1996 (as Pe. lethifera)] – Pe. lugubris [Ruchin & Antropov 2019],[Paukkunen et al. 2015],[Peeters et al. 2004] – Pe. rugifer [Strumia 1997 (as Pe. rugifera)],[Bohart & Menke 1976] Psenulus – Ps. pallipes [Ruchin & Antropov 2019],[Paukkunen et al. 2015],[Strumia 1997],[Woydak 1996] – Ps. schencki [Kolesnikov & Kolesnikova 1974] Stigmus [Krombein 1967]

Prey species outside the Netherlands:

Spheciformes (Digger wasps)

Pemphredonidae Passaloecus – Pa. cuspidatus [O’Neill & O’Neill 2018],[Strumia 1997],[Fricke 1992],[Evans 1973],[Krombein 1967] – Pa. monilicornis [Krombein 1967 (as Pa. ithacae)] – Pa. turionum [Paukkunen et al. 2015],[Blösch 2000],[Strumia 1997],[Woydak 1996]

5. PARASITIC RELATIONS

The following species and groups occurring in the Netherlands ^{[Soortenregister]} are mentioned in literature:

–

–

Parasitic species outside the Netherlands:

–

–

6. IDENTIFICATION

Length males: 3 – 6 mm
Length females: 3 – 6 mm

Genus

The genus Omalus can be identified using the following characters:

1.  Abdomen: with three visible terga, often completely metallic ^{[Paukkunen et al. 2015]}

2. Abdomen: apical edge tergum III without teeth, and without notch ^{[Paukkunen et al. 2015]}

3. Forewing: base radial vein curved ^{[Paukkunen et al. 2015]}

4. Forewing: medial vein slightly curved ^{[Paukkunen et al. 2015]} (ie. an angle larger than 90°, a strong curved vein has an angle of 90°)

5. Head and mesosoma with short pubescence, setae not longer than twice the mid-occellus diameter ^{[Paukkunen et al. 2015]}

6. Head: temples angular viewed dorsally ^{[Paukkunen et al. 2015]}

7. Thorax: metascutellum not elevated ^{[Paukkunen et al. 2015]}

8. Thorax: ventral margin mesopleuron, projecting lightly ^{[Paukkunen et al. 2015]}, tip edges construct obtuse angle.

9. Thorax: fine puctation on the mesoscutum ^{[Paukkunen et al. 2015]}

10. Thorax: sparse and fine punctation on pronotum (sometimes coarser) ^{[Paukkunen et al. 2015]}

11. Legs: tarsal claws with more then one sub-apical tooth ^{[Paukkunen et al. 2015]}

---

---

1. Thorax: mesoscutum shining with tiny punctures or no punctures ^{[Paukkunen et al. 2015]}

2. Abdomen: apical notch shallow ^{[Paukkunen et al. 2015]}

3. Pronotum: setae laterally less than twice as long as diameter of mid-ocellus ^{[Paukkunen et al. 2015]}

4. Antennae: flagellomeres as long as or slightly longer than broad ^{[Paukkunen et al. 2015]}

---

---

–

---

1. Body entirely blue, violet or green ^{[Paukkunen et al. 2015]}

HEAD

no characters

THORAX

no characters

ABDOMEN

no characters

---

---

–

---

1. Body dorsally black, with blue or green reflections ventrally ^{[Paukkunen et al. 2015]}

HEAD

no characters

THORAX

no characters

ABDOMEN

no characters

---

---

Literature

^{Blösch 2000} Blösch, M., 2000. Die Grabwespen Deutschlands – Lebens‐weise, Verhalten, Verbreitung. 71. Teil. In Dahl, F.: Die Tierwelt Deutschlands. Begr.: 1925. – Keltern (Goecke & Evers). – 480 S. 341 Farbfotos. ISBN 3‐931374‐26‐2 (hardcover). DM 98,–. Zool. Reihe, 78: 353-353. https://doi.org/10.1002/mmnz.20020780208

^{Bohart & Menke 1976} Bohart, R.M. & Menke A.S., 1976. Sphecid wasps of the world: a generic revision. - University of California Press, 695 p.

^{Evans 1973} Evans, H. E., 1973. Further studies on the wasps of Jackson Hole, Wyoming (Hymenoptera, Aculeata). The Great Basin Naturalist, 147-155.

^{Fardiansah et al. 2024} Fardiansah, R., Rehling, F., Rappa, N., Dormann, C., & Klein, A. M., 2024. Host identity, nest quality, and parasitism strategy: influences on body size variation in parasitoid bees and wasps. Authorea Preprints.

^{Fricke 1992} Fricke, J. M., 1992. Factors Influencing Length and Volume of Cells Provisioned by Two Passaloecus Species (Hymemoptera: Sphecidae). The Great Lakes Entomologist, 25(2), 8.

^{Kolesnikov & Kolesnikova 1974} Kolesnikov, V. A., & Kolesnikova, N. A. 1974. On the biology of Psenulus. Zashchita Rastenii, 1974, No. No.9, 50

^{Krombein 1967} Krombein, K.V., 1967. Trap-nesting wasps and bees. Life histories, nests and associates. - Washington, DC Smithsonian Inst. Press, 570p.

^{Lomholdt 1973} Lomholdt, O. (1973). Biological observations on the digger-wasp Passaloecus eremita Kohl. Videnskabelige meddelelser fra Dansk naturhistorisk forening i København, 136, 29-41.

^{Lomholdt 1984} Lomholdt, O., 1984. The Sphecidae (Hymenoptera) of Fennoscandia and Denmark. Fauna Entomologica Scandinavica, 4.1: 2.

^{Morgan 1984} Morgan, D., 1984. Cuckoo-wasps. Hymenoptera, Chrysididae. Royal Entomological Society of London. Handbooks for the identification of British insects Volume 6 Part 5. 37p

^{Paukkunen et al. 2015} Paukkunen, J., Berg, A., Soon, V., Ødegaard, F., & Rosa, P., 2015. An illustrated key to the cuckoo wasps (Hymenoptera, Chrysididae) of the Nordic and Baltic countries, with description of a new species. ZooKeys, (548), 1.

^{Peeters et al. 2004} Peeters, T.M.J., C. van Achterberg, W.R.B. Heitmans, W.F. Klein, V. Lefeber, A.J. van Loon, A.A. Mabelis, H. Nieuwen-huijsen, M. Reemer, J. de Rond, J. Smit, H.H.W. Velthuis, 2004. De wespen en mieren van Nederland (Hymenoptera: Aculeata). – Nederlandse Fauna 6. Nationaal Natuurhistorisch Museum Naturalis, Leiden, knnv Uitgeverij, Utrecht & European Invertebrate Survey – Nederland, Leiden.

^{Ruchin & Antropov 2019} Ruchin, A. & Antropov, A., 2019. Wasp fauna (Hymenoptera: Bethylidae, Chrysididae, Dryinidae, Tiphiidae, Mutillidae, Scoliidae, Pompilidae, Vespidae, Sphecidae, Crabronidae & Trigonalyidae) of Mordovia State Nature Reserve and its surroundings in Russia. Journal of Threatened Taxa. 11. 13195-13250. 10.11609/jott.4216.11.2.13195-13250.

^{Soortenregister} Nederlands Soortenregister

^{Strumia 1997} Strumia, F., 1997. Alcune osservazioni sugli ospiti di imenotteri crisididi (Hymenoptera: Chrysididae). Frustula Entomologica, NS, 20(33), 178-183.

^{Tormos et al. 1999} Tormos, J., Krombein, K. V., Asís, J. D., & Gayubo, S. F., 1999. Description of preimaginal instars of four species of Elampini, with some notes on the phylogenetic importance of larval characters in this tribe (Hymenoptera: Chrysididae), Entomological contributions in memory of Byron A. Alexander (Issue 24, p. iii). Natural History Museum, the University of Kansas, p151-155. https://www.biodiversitylibrary.org/page/3272523

^{Waarneming.nl} Waarneming.nl

^{Wei et al. 2014} Wei, N. S., Rosa, P., Liu, J. X., & Xu, Z. F., 2014. The genus Omalus Panzer, 1801 (Hymenoptera, Chrysididae) from China, with descriptions of four new species. ZooKeys, (407), 29–54. https://doi.org/10.3897/zookeys.407.7531

^{Winterhagen 2015} Winterhagen, P., 2015. Strategy for sneaking into a host's home: The cuckoo wasp Omalus biaccinctus (Hymenoptera: Chrysididae) inserts its eggs into living aphids that are the prey of its host. European Journal of Entomology, 112(3), 557.

^{Woydak 1996} Woydak, H., 1996. Hymenoptera Aculeata Westfalica Familia: Sphecidae (Grabwespen), 3-135.

Citation

Krischan, O.R., 2025. Omalus aeneus. Kerfdier, www.kerfdier.nl. Accessed on 17 March 2025.