Amara ovata

When I keyed this using Duff I got to Amara montivaga/nitida, but realised it was not right for either. For montivaga it lacked the sharp dorsal keel on antennomere 2 and for nitida the shape of the pronotum was wrong. Using Hackston I keyed it to montivaga, but I still wasn't convinced it could be. Later I found a second specimen which gave me the same problems, altough it was slightly different in other respects. By now I was pretty much convinced they weren't montivaga, and comparing them to specimens of montivaga in a friend's collection I was even more sure (they were smaller for starters - my ovata was around 8.4/8.5mm long). But where I had gone wrong, and what they were, remained a mystery. I checked back through the keys again and again and could not figure it out.

Happily, I had an opportunity to pass this one to Martin Collier and he very quickly informed me that it was ovata. So now my task was to work out why I had missed this, and I think I now understand that.

Both Duff and Hackston differentiate montivaga and nitida from ovata and similata by the position of the bothrium (Duff) or the puncture it sits in (Hackston) at the hind corners of the pronotum. According to Duff the bothrium is separated from the side margin by no more than 2.5 times the width of the side margin in ovata/similata and at least 2.5 times in montivaga/nitida. Hackston makes the same point in a different way: "Bristle-bearing puncture near the hind angles of the pronotum at least 1.5 times its diameter from the side margin" for montivaga/nitida and "most slightly removed from the margin, usually inserted right on the hind angle" for ovata/similata. In my defence, looking at my photos (and the second specimen) I still think the bristle is at least 2.5 times the width of the side margin from the side and the puncture is slightly more than 1.5x the width of the puncture from the side margin. Moreover, both keys are accompanied by diagrams to illustrate the point (both apparently using the same diagrams) and compared to these mine is clearly closer to what is shown for nitida than for ovata. However, looking at my friend's specimens of montivaga and photos online I can now see that on those the bothrium and its puncture are considerably further away from the side than they are on my two beetles. So I can now see why mine is ovata (and the second was similata) but I don't think the difference is well-described in the keys, and especially not well-depicted.

Amara ovata showing scutellary pore (arrowed red), distance of hind angle bothrium (arrowed yellow) from margin, fore angle of pronotum and second antennal segments at various orientations, Wendling Beck Environment Project (Norfolk, UK), 29th April 2023