Spilomena troglodytes 
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3. Plant relations
4. Prey relations
5. Parasitic relations
Spilomena troglodytes is a rare wasp  occurring throughout the Netherlands [3,9] with an exception of the coastal provinces and the wadden islands . It is the most common representative of the genus in the Netherlands .
The species is active from beginning of June to half September .
Males frequently can be found swarming around bushes and trees [3,12].
Females nest in existing cavities [3,4,5,9,12] in old wood [4,5,9,12], twigs  and abandoned beetle boreholes [9,12], with a preference  of those made by Anobium sp. (Anobiidae) [3,12] (Anobium rufipes , Microbregma emarginatum ). She will gnaw her own nest as well in the marrow of plant stems .
Existing boreholes are cleaned before use [3,12]. Gnawed corridors are about 4-12cm in length . The corridors have a diameter of 1,0-1,4mm [5,8] and a length of 3,5-6 mm .
The brood cells are placed sequentially in a row within the nest cavity [3,5,12]. The brood cells are separated by a 1-2mm thick bulkhead made of wood dust  or a 0,2-7mm wedge-shaped pith plug . Every cell contains 50-60 thrips [3,12]. Cells for females and males are equal in size .
The filled nest is closed with a wood pulp plug that is tamped using the abdomen [3,13]. The outermost layer is fortified by mixing the wood pulp with saliva that hardens as it dries  into a somewhat shiny disc .
Females find their nest using smell and as a result normally take a lot of time to find it after returning from the hunt, which is typical in the genus Spilomena [5,12]. They will scout around a large surface around the assumed nest position until they smelled it out using the antennae 
The development time of the relatively large (1,25 mm), weakly saussage-like bent  egg is unknown. The matt white cocoons are attached to the cell wall and occupy almost the entire cell length .
The male and female brood cells are randomly placed in the nest cavity . There are more female than male cells which results in a surplus of female over males in a ratio of 2:1 .
2.3. BEE HOTEL
The males as well as the females can be found on bee hotels. Females use them to nest.
From my own observation of a male arriving early in the evening I suspect the males to use empty boreholes as resting place, see here.
Most Crabronidae females produce one generation per year .
The prey is transported using the mandibles [4,12].
3. PLANT RELATIONS
The following wood types are mentioned in literature as medium for the wasp to built her nests in:
Sambucus (Elder) 
Alnus (Elm) 
Betula (Birch) 
Carpinus (Hornbeam) 
Picea abies (Norway spruce) 
Crataegus (Hawthorn) 
Rubus (Bramble) [7,8]
|Salix (Willow) |
Aesculus (Horse chestnut)
– Horse chestnut (Aesculus hippocastanum) 
Fence poles  or thatched roofs  may be used as well.
Males feed with honeydew that is licked from leafs.
The following wood types are mentioned in literature as foodsources:
– Angelica archangelica 
In the garden Foeniculum vulgare is present but I have not observed the species on it.
4. PREY RELATIONS
The species uses mainly nymphs of thrips (Thysanoptera) for her brood [3,4,5,9,12]. Observations have been reported on the use of Psyllids (Psyllidae) nymphs  and the nymphs of Scale insects (Coccidae) and Aphids (Aphidoidea) .
The following species and group occurring in the Netherlands  are mentioned in literature:
|Aphidoidea (Aphids) [4,5]|
|Coccidae (Scale insects) [4,5]|
|Psyllidae (Psyllids) |
|Thysanoptera (Thrips) |
At least Thrips and Aphids are present in the garden.
5. PARASITIC RELATIONS
The following species and group occurring in the Netherlands [1, 2(Oscinella nigerrima)] are mentioned in literature:
Ichneumonidae (Ichneumon wasps)
– Neorhacodes enslini [3,8,10,12]
Chalcidoidea (Chalcid wasps)
– Torymus armatus [3,8(as Diomorus armatus)]
Chloropidae (Frit flies)
– Oscinella nigerrima 
Length males: 2 – 3 mm
Length females: 2,5 – 3 mm
The genus Spilomena can be identified using the following characters:
1. Forewing: with two submarginal cells [9,10,11]
2. Forewing: submarginal cell 2 not petiolate [9,10,11]
3. Forewing: pterostigma large and almost semicircular [9,10,11]
4. Forewing: radial cell longer than pterostigma [9,10,11]
5. Forewing: radial cell tip sharp [9,10,11]
6. Forewing: with one discoidal cell [9,10,11]
7. Abdomen: first abdominal segment not petiolate [9,10,11]
8. Abdomen: entirely black [9,10,11]
1. Antenna with 12 segments [9,10,11]
2. Abdomen with 6 segments [9,10,11]
1. Clypeus evenly rounded 
2. Mandible usually light brown, seldom dark brown 
3. Ratio distance between hind ocelli (POL) : distance hind ocellus to eye edge (OOL) = 1,4 – 2,0 [10,11]
4. Back head less strongly developed 
1. Frontal scutellem furrow narrow and without transverse carinae [10,11]
2. Apical edge mesonotum without longitudinal grooves 
3. Wing veins brown 
4. Dorsal field propodeum not limited by carina, at least at the base with net-like wrinkles between the main sculpture 
- Tergite 6 with double longitidunal carina 
specimen caught for identification on 10-vi-2021, length ±3mm
1. Antenna with 13 segments [9,10,11]
2. Abdomen with 7 segments [9,10,11]
3. Face and clypeus yellow, at least the front edge yellow (here face and clypeus) [9,10,11]
1. Frontal edge clypeus not or lightly indented (here lightly indented) [10,11]
2. Mandible distally with small red-brown spot [10,11]
3. Clypeus entirely or almost entirely yellow [9,10]
4. Ratio distance between hind ocelli (POL) : distance hind ocellus to inner eye edge (OOL) = 1,4 – 2,0 (here ±1,4) [10,11]
5. Antennal members clearly restricted, bead-like [9,10,11]
6. Antennal flag dark, at most more or less red-brown on the inside 
1. Frontal scutellum furrow narrow and without transverse carinae [9,10,11]
2. Dorsal field propodeum not limited by carina [9,10,11], at least at base with fine net-like wrinkles between the main sculpture 
no specific characters
References1 Nederlands Soortenregister
3 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.
4 BOHART, Richard M.; BOHART, Richard Mitchell; MENKE, Arnold S. Sphecid wasps of the world: a generic revision. Univ of California Press, 1976.
5 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
6 Vikberg, Veli. (2000). A re-evaluation of five European species of Spilomena with a key to European species and relevance to the fauna of North Europe, especially Finland (Hymenoptera : Pemphredonidae). Entomologica Fennica. 11. 35-55. 10.33338/ef.84044.
7 VAN LITH, J. P. De Nederlandse Spilomena-soorten (Hym. Sphecidae). Entomologische Berichten, 1955, 15.24: 525-527.
8 DANKS, Hugh V. Biology of some stem‐nesting aculeate Hymenoptera. Transactions of the Royal Entomological Society of London, 1971, 122.11: 323-395.
9 KLEIN, Wim. De graafwespen van de Benelux. Jeugdbondsuitgeverij, Utrecht, 1996, 1-130. + KLEIN, Wim. De graafwespen van de Benelux: supplement. Jeugdbondsuitgeverij, 1999.
10 JACOBS, H. J (2007): Die Grabwespen Deutschlands Ampulicidae. Sphecidae, Crabronidae–Bestimmungsschlüssel in Blank, SM & Taeger, A (Hrsg): Die Tierwelt Deutschlands und der angrenzenden Meeresteile nach ihren Merkmalen und nach ihrer Lebensweise, Hymenoptera III–Keltern, Goecke & Evers, 79: 1-207.
11 Hermann Dollfuss, "Bestimmungsschlüssel der Grabwespen Nord- und Zentraleuropas (Hymenoptera, Sphecidae) mit speziellen Angaben zur Grabwespenfauna Österreichs", Publikation der Botanischen Arbeitsgemeinschaft am O.Ö.Landesmuseum Linz, LINZ, 20. Dezember 1991
12 LOMHOLDT, O. 1975-1976; 1984 (2. Auflage). The Sphecidae (Hymenoptera) of Fennoscandia and Denmark. Fauna Entomologica Scandinavica, 4.1: 2.