Mason wasp: Ancistrocerus nigricornis?

[NickU]

Can anyone identify this smart black and yellow mason wasp with certainty from these photos, taken today 10.5.10 in Wiltshire. Size similar to common wasp worker.

From online photos, it looks to me most like Ancistrocerus nigricornis, but this seems to be a declining species form what I've read. Maybe it's the commoner E.parietum, but the marks on the first abdominal segment don't look quite right. Maybe it's something else entirely?!

Nick Upton - naturalist/photographer

[Geoff F]

Looks OK according to my book. Brownish tarsi and the first yellow abdominal band has a square notch cut out.

But a clear view of the wings will be needed to rule out A. gazella which has a dark smudge near the wing tip.

[oxycera]

Forget the book, these are microscope jobs, but yes, I think you are correct with Ancistrocerus.

[NickU]

Many thanks to you both for feedback and suggestions. In case it helps, here are some different views of the head pattern and the clearest wing shot I have. To me the head and wing patttern do match very closely with what I can find for female A. nigricornis eg see: Iconographie des Vespidae du Monde

In the pics I've found A. gazella doesn't match so well, but I don't know how variable head, wing and first abdominal segment patterns are in this genus.

[eucera]

The first break in the RES keys (the best for UK Eumenids) is based on the relative shapes if the second gastral sternite, and the sculptation of the propodeum. Ancistrocerus is a really difficult genus, and the characters are microscopic and (I believe the word is) subtle.

I would never accept a record based purely on a photograph

[NickU]

OK, many thanks, I'm happy to call it Ancistrocercus sp. if microsposcopy is needed to be sure of the species, and it sounds like it is! Nice wasp, though, and one I haven't seen before. Hope I can discover a nest this summer.
Nick

[watsthat]

Originally Posted by oxycera

Forget the book, these are microscope jobs, but yes, I think you are correct with Ancistrocerus.

I have recently been looking at a similar (not identical) wasp that I took a pic of on 25.07.10. I have done a little research and I think it is also Ancistrocerus sp. Info obtained suggests that this family have hooked antennae (ie curved at the tip) but the subject of this thread appears to have straight antennae.
Would this attribute rule out Ancistrocerus or is it a diagnostically unreliable feature?
Any comments would be gratefully appreciated.


Cheers

Pete

[watsthat]

Ahh... how embarrassing, I`ve just double checked, it could be a female

I`ll get my coat

Pete

[oxycera]

pitfalls are everywhere in entomology...

[eucera]

The wasp in the pic is certainly a female (far too little yellow on the face for a male).

I would be very reluctant to do Ancistrocerus to species from photos - they are bad enough when handling museum material