Aneugmenus temporalis

This individual was swept from Bracken but that doesn't help narrow the ID down as all four Aneugmenus species feed on Bracken. I initially identified it tenatively as padi (the only common species), but noting some reservations as the extent of carina at the side of the head suggested temporalis.

The RES key first eliminates fuerstenbergensis, and I was happy I elimated that correctly, although on first look I overlooked the white labrum (white is an exaggeration on my dried specimen - perhaps it was white in life but this isn't visible in any of my live photos). With the entirely black abdomen (other than a faintly pale area towards the base) I was pretty confident I've correctly eliminated coronatus too, though some of the characters in the key are hard to interpret without comparative material. My real challenge was differentiating padi from temporalis. The key uses two characters - the degree of concavity and definition of the frontal area and the extent of the occipital carina (at least I think that's what it means although it doesn't use that term).

There are various ridges and dips in the surface of the front of the head but these include a moderately well-defined area which seems pretty concave in the middle, which I thought pointed to padi, though frankly this area was pretty hard to see and be sure precisely what it was supposed to look like in each species. But I found it really hard to see the occipital carina. Removing the head and looking at various angles I could see that it is clearly-defined and fairly sharp in the lower half (up to the red arrow in image below, from the right side) about half-way up the eye. That's as far as it should go on temporalis, but on padi it should extend to level with the top of the eye. It does continue vaguely a little farther (to the blue arrow on my photo) but that's still well short of the top of the eye. I can't make it out at all any further than that. So that seemed better for temporalis.

The British Sawflies website says that on temporalis "the distance between cenchri is less than the width of a cenchrus, the cenchri themselves being elongate (3:1)." Well, the conchri are fairly elongate but 2.5:1 not 3:1, and their distance apart is much more than their width. Unfortunately it doesn't say what these should be on padi, but it did at least seem to eliminate temporalis and that only leaves the more expected padi.

At this point I did two things - order Sawflies of Europe by Jean Lacourt and contact county sawfly recorder Andy Musgrove. Andy thought it might actually be temporalis because in his experience the carina is easy to see on padi, plus the legs are usually more yellow.

Lacourt's book arrived next day and here the description of the difference conchri shape and spacing is described differently: "considerably elongated" and "the distance between them less than 2 times their length" for temporalis vs. "normal" and "3 times their length" for padi. I can't make sense of the distance thing to be honest, but Lacourt has also included diagrams of the saws, and this seems to clinch it as temporalis.

female Aneugmenus temporalis showing its wings, labrum, occipital carina, front of head, cenchri, upper side of abdome and saw (including close-up of tip), Barrow Common (Norfolk, UK), 10th June 2022