Ophion crassicornis

Gavin Broad's key to nocturnal Ichneumonidae distinguishes between crassicornis Brock and ?crassicornis Brock northern ‘morph’. I'm not sure if I'm reading too much into this or not, but I guess that means he thinks two species may be involved, albeit one as yet undescribed. Although Norfolk isn't all that far north, the ones I've found so far have all keyed to ?crassicornis Brock northern ‘morph’. The review of the Swedish Ophion by Johansson and Cederberg describes two new species which are closely related to crassicornis, angularis and borealis. I wondered if either of those might equate to Broad's "northern 'morph'" but it uses different characters to distinguish between them so I think not. Using Johansson and Cederberg mine key to crassicornis.

I intially used Gavin Broad's key to identify these two ichneumons, but not without difficulty. My first question was at couplet 3 where I quibbled over the strength of the yellow membrane. It doesn't show on the photos here very well, but it was pretty obvious looking at the two insects - "slightly fuscate/yellowish" didn't seem to me to do it justice. But that's subjective and it certainly wasn't ventricosus which I had very recently identified and looks very different (and did indeed have even stronger yellow wings). So a wobble but able to move on easily from that.

Another minor challenge at couplet 7 was again subjective - the yellow around the eyes of my specimens was sufficiently clear to me that I didn't think "Lacking yellow markings, although sometimes with ill-defined paler areas" was an accurate description. But there was no yellow on the mesoscutum or the ptersostigma so it was clear enough which way I had to go here.

Understanding the difference in mandibular gape shape was more of a challenge at couplet 8. To my eyes it was slightly acute and looked nothing like the diagram in Fig 6. But the other characters were wrong for luteus - I'm so grateful that Gavin Broad uses multiple characters in most of his couplets - it really helps at times like this.

Next couplet (9), next problem. I thought the pleurosternal angles were clearly anterior to sternal angles as shown in Fig. 10 but the pleurosternal angles were right-angled as Fig. 9. Again an additional character helped here - the first flagellomere was much less than 3x its width.

I then had a look at the review of the Swedish Ophion by Johansson and Cederberg and was reassured to see a photo of crassicornis there which had the same shape of the epicnemial carina as mine, thus removing my biggest concern keying mine. I took the two specimens through this key and although one or two of the minor issues I'd had with Broad's key remained, I ended up pretty firmly on crassicornis (although on one of them the curvature of the anterior transverse carina of propodeum was far from convincing).

In the photos below each pair of images show both specimens and in each case the first of each pair is always the same specimen and the second of the pair is the other specimen. The first one had 59 flagellomeres on each antenna and the second had 58 on each antenna.

2x Ophion crassicornis showing mandibles, hind trochantellus, epicnemial carina, first flagellomeres, gap between outer ocellus and compound eye, distances between tentorial pits and compound eye (ignore the units - microscope was at an uncallibrated zoom here), facial punctures, mesopleural wrinkles and propodeum, Wendling Beck Environment Project (Norfolk, UK), 25th May 2023

I had previously identified this one as crassicornis using Broad's key and I recall that that one also keyed out to ?crassicornis Brock northern ‘morph’.

Ophion crassicornis showing base of antenna and face, North Elmham Cathedral Meadows (Norfolk, UK), 17th May 2020

These were a bit quicker to ID following my experience above. In the photos below each pair of images show both specimens and in each case the first of each pair is always the same specimen and the second of the pair is the other specimen. The first one had 58 flagellomeres. The second had 61 flagellomeres but I don't think the trochantellus proportions were very different so I assume it is the same taxon.

2x Ophion crassicornis showing mandibles, forewings, hind femora, hind trochantellus, epicnemial carinas, first flagellomeres and head from above, Wendling Beck Environment Project (Norfolk, UK), 11th June 2023

The next three were from a different site (within the same project area) the same night. This first one had 55 flagellomeres.

Ophion crassicornis showing forewing, head from above, mandibles, antenna and epicnemial carinas, Wendling Beck Environment Project (Norfolk, UK), 11th June 2023

The second had 56 flagellomeres.

second Ophion crassicornis showing forewing, head from above, mandibles and epicnemial carinas, Wendling Beck Environment Project (Norfolk, UK), 11th June 2023

The third had 58 flagellomeres.

third Ophion crassicornis showing forewing, head from above, mandibles, antenna and epicnemial carinas, Wendling Beck Environment Project (Norfolk, UK), 11th June 2023