Working with a live specimen

On Friday I found this potter wasp (one of the small, solitary nesting wasps) running around on the landscape contractor's bright green car. I thought I'd have a crack at identifying it to species using just a hand lens, which turned out to be an arduous way to spend a Saturday...

Step 1:  Put wasp in tube into the fridge to anesthetise

Step 2: Take out the book on solitary wasps

Step 3: Turn to first key in book, take chilled wasp out the fridge, start keying...

It seems that everything pretty well matches the family Eumenidae, which takes me to the next part of the book...

Step 4: Keying from the Eumenidae, following on until we get to couplet 7, which is over to the next page.

Oh no!

Ah jeez.

Step 5: Get stool from kitchen, retrieve tiny wasp from ceiling.

She's back in the tube and she's angry.

Quickly, to the next page....

It looks like she's an Ancistrocerus! We are getting there.

Step 6: Continuing on to try to get her down to species...

Hmm, a groove or step on 2nd ventral plate.... Is this it?

To me it looks like there is a step, but then a bulge. It's very difficult to get a decent picture in the hand and at the correct angle. Even after putting her back in the fridge for a while, she simply warms up again very quickly and dashes about.

Might she be Ancistrocerus nigricornis?

I'm just not sure whether this is simply the normal join between two ventral plates on the abdomen. Looking ahead in the rest of the key, it refers to the underside of the 2nd ventral plate, but my pictures are not clear enough. This is where we get stuck without using a microscope and other preserved specimens for comparison.

For many small invertebrates, photographs can only really take you so far in terms of identification, so I'll be told by entomologists that I should have kept the specimen. But seeing as I have a backlog of other material to microscope...

See ya Ancistrocerus sp., back to caterpillar hunting you go.