CONTENTS

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

1. DISTRIBUTION

The wasp Ectemnius cavifrons ^{[Soortenregister]} is uncommon and occurs throughout the Netherlands ^{[Waarneming.nl]}.

2. BEHAVIOUR

2.1. ACTIVITY

The species is active from half April up to end September ^{[Peeters et al. 2004]}.

2.2. DEVELOPMENT

Her widely branched nests are gnawed in rotting and dead wood ^{[Peeters et al. 2004],[Blösch 2000]}, but old tunnels from a previous season can also be re-used ^{[Blösch 2000]}.
A nest location can reside in a completely shades location ^{[Jacobi 2001]}.

The nest starts with a straight corridor that branches after several centimetres in up to thirteen side corridors that can reach 30-70 cm in depth, sometimes even up to 120 cm ^{[Blösch 2000]}. At the end of these tunnels a brood cell is located that measures 8-10 (h) x 12-15 (l) cm ^{[Blösch 2000]}.

Two females may use the same entrance but each will gnaw it’s own corridors ^{[Blösch 2000]}. It is also possible that numerous females will nest in a nest aggregation ^{[Gabel et al. 2018]}.

The larvae are fed flies, about 6-12 prey species per brood cell ^{[Blösch 2000]}.  After the brood cells are filled the corridors are filled up with wood pulp ^{[Blösch 2000]}.

After about three days the eggs will hatch ^{[Hamm & Richards 1926],[Lomholdt 1984]}, and the following development of the larva will take two to three weeks ^{[Lomholdt 1984]}. Then a cocoon is spun in which the larva hibernates ^{[Lomholdt 1984]}. The pupal development will take two to three weeks ^{[Lomholdt 1984]}, followed by the emergence of the adult which will live for two to three months ^{[Lomholdt 1984]}.

One generation is produced per year, but in long summers two generations are possible ^{[Blösch 2000]}.

2.3. BEE HOTEL

Sleep and shelter
The males will use the bee hotels as sleeping place ^{[Breugel 2014],[Jacobi 2001]}. Occasionally a fresh female without a nest may do so as well ^{[Breugel 2014],[Jacobi 2001]}.

On numerous occasions I have observed how a male that is searches for a suitable spot will hang around the hotels for quite some time, land below an opening, throw a quick glance to inspect the potential spot and take off again. He will land with the antennae directed towards the entrance to sniff it out and crawl head first partially, or entirely inside.
It can take a large part of an hour before the right spot has been found, in which case he will crawl out backwards from the tunnel, turn in front of the entrance and crawl in backwards again so it’s head is pointed towards the entrance when inside.

Aggression
From my own observations it turns out that the males looking for a spot on the bee hotel are aggressive towards the other bees and wasps on the hotels. When they see an insect they want to scare away they will align themselves in the air with the victim, shoot forward quickly and crash into them. They seem to do this especially with insects near holes in order to scare them away. But they will also attack insects approaching a nest hole in flight. Especially European wool carder bees (Anthidium manicatum) are targeted although these do not seem to be impressed by the harassments.
I have caught a few of these aggressive males for identification and they were all E. cavifrons.

2.4. MATING

The males will look for females either actively or passively. In the latter case he will wait in the morning on a sunny leaf on which he put a scent-marking, until a female will pass by ^{[Jacobi 2001]}. The scent-markings are deposited on the leaf by dragging with their abdomen ^{[Jacobi 2001]}.

On the warmer hours of the day he will actively patrol nearby suitable nest locations for females suitable for mating ^{[Jacobi 2001]}.

Once a female is located he will land on her back and grabs her above the wing base with his middle legs ^{[Jacobi 2001]}. The front legs are resting over the female’s head with the tarsi along the inner eye edge. As long as the female keeps her wings closed the male will keep his body straightened and his hind legs bend alongside her body so they do not touch the wings ^{[Jacobi 2001]}.

The way he embraces her wings makes it possible for her to still use them, and they may fly up together during mating ^{[Jacobi 2001]}.

When the female opens her wings he will extend his abdomen exposing his genitals, and simultaneously she will bend her body upwards so the genitals meet ^{[Jacobi 2001]}. Mating may take as long as a few seconds or many minutes ^{[Jacobi 2001]}. after which the bond of the genitals is broken and she will close her wings again ^{[Jacobi 2001]}.

During mating the males keeps his jaws open so the long palps rest on her stirn and the front legs still positioned in the inner edge of the eyes ^{[Jacobi 2001]}. During this process the antennae are positioned parallel and downwards with those of the female between them ^{[Jacobi 2001]}. The shape of Ectemnius male antennae often have rather deep recesses will help to lock them with those of the female ^{[Jacobi 2001]}. This recesses are species specific ^{[Klein 1999],[Blösch 2000],[Jacobi 2001]}, and may have a function during partners selection by the female ^{[Jacobi 2001]}.

Crabronidae females probably mate only once ^{[Lomholdt 1984]}.

2.5. HUNTING

Hunting area

The female has a area in which she will hunt for prey. Throughout it she has a number of lookout positions that are located at the height of the flower horizon or lower looking so she can observe the flower visitors ^{[Jacobi 2001]}. The outlook positions are used alternately during a period ^{[Jacobi 2001]}.

Like all Ectemnius females she may also actively hunt by flight, during which she will slowly cruise through the herb layer hovering still near flowers ^{[Jacobi 2001],[Lomholdt 1984]}. When she has spotted a prey she will slowly approach and, in case of a positive identification, explosively accelerate towards the prey and grab it with open front legs and mandibles ^{[Lomholdt 1984]}. This is learned behaviour that she will learn by trial and error ^{[Lomholdt 1984]}.

The hunting area may be shared by multiple females ^{[Jacobi 2001]}. In the rare occasion two females want to use the same outlook position, the new arrival will bump into the present female which will be followed by a staring contents in which the looser will take off ^{[Jacobi 2001]}.

Prey recognition

Probably Ectemnius sees sharp on a distance of about 15 – 20 cm ^{[Lomholdt 1984]}.

The female will respond to a potential prey when it enters her field of vision which extends from a few centimetres to about 2 meters ^{[Jacobi 2001]}. Small insects she will follow by moving her head, larger insects and those on flowers will have her take off to have a closer look ^{[Jacobi 2001]}. On a distance of about 4 centimetres she will determine if she has found a prey, when positive she will accelerate explosively and throw herself onto the prey and grab it tumbling down to the ground and land somewhere in the foliage ^{[Jacobi 2001]}.
It is not clear whether she will use her sense of smell to recognize prey ^{[Jacobi 2001]}.

Prey handling and transport

The females will keep the caught prey perpendicular underneath her body with her hind and middle legs so the head will extend on one side of her body and the abdomen on the other, the wasp’s sternites are positioned above the thorax of the fly ^{[Jacobi 2001]}. Grabbing herself with the front legs she will sting the fly in the chest ^{[Jacobi 2001]}.
When the fly is paralysed she will turn it underneath and align it with her abdomen, the abdomen of the fly sticking out underneath her abdomen ^{[Jacobi 2001]}. During flight the middle legs clamp the neck and the hind legs are used to stabilize the prey ^{[Jacobi 2001]}. The free front legs are use during landing near the nest entrance after which she will drag the prey into the nest ^{[Jacobi 2001]}.

A hunting sortie will take around 10-15 minutes and when the wasp returns on the nest she will exit for the next sortie in 30s to several minutes ^{[Pickard 1975],[Hamm & Richards 1926]}.

3. FOOD PLANTS

Adult wasps feed with nectar. The following plant groups and species are cited in literature as food plants:

Apicaceae (Umbellifers) [Peeters et al. 2004],[Klein 1999],[Blösch 2000]	Angelica [Woydak 1996] – Angelica sylvestris (Wild angelica) [Waarneming.nl] Pastinaca [Woydak 1996] – Pastinaca sativa (Parsnip) [Waarneming.nl] Heracleum [Woydak 1996] – Heracleum sphondylium (Hogweed) [Waarneming.nl]
Asteraceae (Composite family) [Peeters et al. 2004]	–

4. PREY RELATIONS

The species ise flies as food for her brood ^{[Peeters et al. 2004],[Klein 1999],[Blösch 2000],[Ruchin & Antropov 2019]}.
The following species and groups occurring in the Netherlands ^{[Soortenregister]} are mentioned in literature:

Diptera (Flies)

Calliphoridae (Blow flies) [Klein 1999],[Blösch 2000],[Ruchin & Antropov 2019] Pollenia – Pollenia rudis [Bland 2003] Calliphora – Calliphora vicina [Bland 2003] Sarcophagidae (Flesh flies) [Ruchin & Antropov 2019] Stratiomyiidae (Soldier flies) [Ruchin & Antropov 2019] Sargus –  Sargus bipunctatus (Twin-spot centurion) [Blösch 2000] Syrphidae (Hover flies) [Peeters et al. 2004],[Klein 1999],[Blösch 2000] Episyrphus [Gabel et al. 2018] – Episyrphus balteatus (Marmalade hoverfly) [Ruchin & Antropov 2019],[Bland 2003],[Hamm & Richards 1926] Eupeodes – Eupeodes corollae [Bland 2003],[Hamm & Richards 1926] – Eupeodes latifasciatus [Bland 2003],[Hamm & Richards 1926] – Eupeodes luniger [Bland 2003] Helophilus – Helophilus pendulus [Hamm & Richards 1926] Leucozona – Leucozona lucorum [Pickard 1975] Melanostoma [Gabel et al. 2018] – Melanostoma mellinum [Pickard 1975],[Hamm & Richards 1926] – Melanostoma scalare [Hamm & Richards 1926] Meliscaeva – Meliscaeva auricollis [Hamm & Richards 1926] Platycheirus – Platycheirus albimanus [Pickard 1975],[Hamm & Richards 1926] – Platycheirus pellatus [Hamm & Richards 1926] – Platycheirus scutatus [Pickard 1975],[Hamm & Richards 1926] Rhingia – Rhingia campestris [Hamm & Richards 1926] Scaeva – Scaeve pyrastri [Pickard 1975],[Hamm & Richards 1926] Syrphus [Gabel et al. 2018] – Syrphus ribesii [Bland 2003],[Hamm & Richards 1926] – Syrphus torvus [Bland 2003] – Syrphus vitripennis [Bland 2003],[Hamm & Richards 1926] Tabanidae (Horse flies) [Klein 1999],[Ruchin & Antropov 2019] Chrysops – Chrysops caecutiens [Hamm & Richards 1926]

Auchenorrhyncha (Cicadas)

Cicadellidae Iassus – Iassus lanio [Ruchin & Antropov 2019],[Bland 2003]

Prey species outside the Netherlands:

–

–

5. PARASITIC RELATIONS

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

Diptera (Flies)	Anthomyiidae (Muscoidea flies) [Blösch 2000] Eustalomyia -Eustalomyia hilaris [Blösch 2000],[Hamm & Richards 1926],[Woydak 1996] Sarcophagidae (Flesh flies) Amobia – Amobia signata [Povolny 1997] Macronychia – Macronychia polyodon [Povolny 1997] – Macronychia striginervis Povolny 1997
Hymenoptera (Wasps)	Chalcididae (Chalcid wasps) Pteromalus [Blösch 2000],[Ruchin & Antropov 2019],[Hamm & Richards 1926] Chrysididae (Cuckoo wasps) Chrysis – Chrysis fulgida [Ruchin & Antropov 2019] Ichneumonidae (Ichneumon wasps) Perithous – Perithous albicinctus [Blösch 2000],[Ruchin & Antropov 2019],[Hamm & Richards 1926]

Another category of parasites are mites which will not further be investigated here. The males often have one or more clusters of these arthropods cling to their bodies, like this one. The mites are attached to the armor and wings and are present all over his body, especially on the abdomen.

Parasitic species outside the Netherlands:

–

–

6. IDENTIFICATION

Length males: 8 – 12 mm
Length females: 9,5 – 14,5 mm

Genus

The genus Ectemnius can be identified using the following characters:

1.  Forewing with one submarginal cell ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

2. Head: ocelli usually form an obtuse isosceles triangle ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

Jacobs ^{[Jacobs 2007]} specifies: often an acute angle.

3. Head: frontally wider than high ^{[Klein 1999],[Dollfuss 1991]}

4. Side thorax, metapleuron (M) and often side propodeum (P), with strong transverse wrinkles ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

5. Thorax: side (mesopleuron) has a short, angular or curved transverse keel in front of middle coxa ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

6. Abdomen: terga smooth with fine punctation, only often slightly stronger on tergite 1 ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

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1. Antennae with 12 segments ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

2. Abdomen with 6 segments ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

HEAD

1. Ocelli: form an isosceles triangle ^{[Klein 1999],[Dollfuss 1991]}

2. Ocelli: distance between hind ocelli (l_oo) < distance between hind ocellus and eye edge (l_oe) ^{[Jacobs 2007]}

3. Vertex: around ocelli clearly dented ^{[Jacobs 2007]}

1. Antenna: segment 3 more than 4x longer than wide ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

4. Antenna: segment 3 is 2x longer than segment 4 ^{[Jacobs 2007]}

7. Clypeus: with golden hairs ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

8. Frons: top of the smooth area above antennal base not confined by a transverse keel ^{[Klein 1999]}

9. Mandible: inner edge without tooth ^{[Jacobs 2007],[Dollfuss 1991]}

10. Mandible: with yellow markings ^{[Dollfuss 1991]}

11. Clypeus: lobe straight ( l₁ ) ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}
12. Clypeus: lobe ( l₁ ) wider than distance to side tooth ( l₂ ) ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

THORAX

1. Mesonotum: frontally punctated, remainder punctated and wrinkled ^{[Jacobs 2007],[Dollfuss 1991]}

2. Side thorax, mesopleuron, wrinkled ^{[Jacobs 2007],[Dollfuss 1991]}

3. Propodeum: sides densely and finely striped, less glossy ^{[Jacobs 2007],[Dollfuss 1991]}

4. Propodeum: side and dorsal side not separated by keels ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

5. Pronotum: edges rounded ^{[Jacobs 2007]}

6. Thorax: with yellow markings ^{[Jacobs 2007]}

7. Underside mesothorax frontally without transverse keel, only developed at the sides ^{[Dollfuss 1991]}

6. Mesonotum and usually tergite 1 with long erect hairs ^{[Dollfuss 1991]}

ABDOMEN

1. Yellow bands abdomen interrupted in the middle ^{[Klein 1999],[Dollfuss 1991]}

2. Sterna: 5 and 6, or 6 black ^{[Jacobs 2007],[Klein 1999]}, sternite 6 sometimes with yellow spots ^{[Jacobs 2007]}

3. Pygidium: black ^{[Jacobs 2007],[Klein 1999]}
4. Tergum 6: with channel-shaped, gutter-shaped, pygidium ^{[Dollfuss 1991]}

Sternite 7 is also, to a lesser extend, remarkably gutter-shaped, but this is not a character for the species.

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1. Antenna with 12 segments ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

2. Abdomen with 7 segments ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

HEAD

1. Antenna: segment 3 more than 3x longer than wide ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

2. Antenna: segment 3 with deeply bulged ^{[Jacobs 2007],[Klein 1999]} and dorsally lightly arched ^{[Jacobs 2007],[Dollfuss 1991]}

3. Antenna: segment 3 with tooth in middle ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

4. Antenna: first tooth on segment 3 without hair bristle ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

5. Antenna: segments 4 and 5 strongly cut out ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

6. Antenna: segment 6 without deformations ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

7. Clypeus: hairs golden ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

8. Mandible: inner edge without tooth ^{[Jacobs 2007],[Dollfuss 1991]}

9. Vertex: in front of ocelli clearly dented across the whole width ^{[Jacobs 2007],[Dollfuss 1991]}

10. Frons: Top smooth area above antennal base not confined by a transverse keel (not a species character)

THORAX

1. Mesonotum: punctated and wrinkled ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

2. Side thorax, mesopleuron, wrinkled ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

3. Propodeum: sides finely striped ^{[Jacobs 2007]}

4. Propodeum: side and dorsal side not separated by keel ^{[Jacobs 2007],[Klein 1999],[Dollfuss 1991]}

5. Thorax: Underside mesothorax frontally without transverse keel ^{[Dollfuss 1991]}

6. Legs: with yellow markings ^{[Jacobs 2007]}

7. Foreleg: trochanter without tooth or high keel ^{[Jacobs 2007],[Klein 1999]}

8. Foreleg: thigh (femur) without tooth ^{[Dollfuss 1991]}

9. Middle leg: inner side basitarsus widened before top ^{[Dollfuss 1991]}

10. Foreleg: tarsal segment 5 strongly widened and rounded ^{[Dollfuss 1991]}

ABDOMEN

1. Tergite 7: without pygidium ^{[Jacobs 2007],[Klein 1999]}

2. Tergum 7: with short hairs, edge curves gradually into sides

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Literature

^{Bland 2003} Bland, K. P., 2003. An observation of the prey species of the solitary wasp, Ectemnius cavifrons (Hymenoptera: Sphecidae).

^{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

^{Breugel 2014} Breugel, P. van., 2014. Gasten van bijenhotels. – EIS Kenniscentrum Insecten en andere ongewervelden & Naturalis Biodiversity Center, Leiden.

^{Dollfuss 1991} Dollfuss, H., 1991. Bestimmungsschlüssel der Grabwespen Nord-und Zentraleuropas. Stapfia, 24, 1-247.

^{Gabel et al. 2018} Gabel, M., Wolters, V., & Jauker, F., 2018. Beobachtungen zum Verproviantierungsverhalten des Wald-Fliegenjägers Ectemnius cavifrons (Thomson, 1870) in einer Nestansammlung auf dem Hoherodskopf (Vogelsbergkreis)(Hymenoptera, Crabronidae). Hessische Faunistische Briefe, 37(1-2), 1-6.

^{Hamm & Richards 1926} Hamm, A. H., & Richards, O. W., 1926. The biology of the British Crabronidae. Transactions of the Royal Entomological Society of London, 74(2), 297-331.

^{Jacobi 2001} Jacobi, B., 2001. Beutefang und Paarungsverhalten bei Ectemnius (Clytochrysus) cavifrons (Thomson, 1870) (Hymenoptera, Sphecidae, Crabroninae). 81 - 88.

^{Jacobs 2007} 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.

^{Klein 1999} Klein, W., 1996. De graafwespen van de Benelux. Jeugdbondsuitgeverij, 1-130. + Klein, W., 1999 De graafwespen van de Benelux: supplement. Jeugdbondsuitgeverij, 1-37.

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

^{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.

^{Pickard 1975} Pickard, R. S., 1975. Relative abundance of syrphyd species in a nest of the wasp Ectemnius cavifrons compared with that in the surrounding habitat. Entomophaga, 20(2), 143-151.

^{Povolny 1997} Povolny, D., 1997. The flesh-flies of Central Europe (Insecta, Diptera, Sarcophagidae). Spixiana Suppl., 24, 1-260.

^{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

^{Waarneming.nl} Waarneming.nl

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