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The carabid beetle genus Ophonus is one that I almost exclusively see whilst light trapping. In fact I have only ever found them through other methods a couple of times, usually from looking in the seed heads of wild carrot.

There are 14 species to be found in the UK. One of them, O. ardiosiacus turns up regularly in the garden over the summer months and on the warmer nights can be pretty common.

I find some of these really difficult to key out. Of the species with sharp pronotal hind angles there comes a point in the key where you need to make a judgement on pronotum width and curviness. It's the couplet that separates O. puncticeps.

For puncticeps it says the pronotum is more narrow, less than 1.3 times as wide as long, sides are little contracted or sinuate towards base.

Other species should key the other way as they should have a wider pronotum, more than 1.3 times as wide as long and it's more sinuate laterally.on the width to length ratio of the pronotum, and also the amount that the edge of the pronotum is sinuate (curvy).

So here are a couple of species of Ophonus. One should key one way, the second, the other. But which one is which?

I'll put you out your misery, the species on the right should have a narrower pronotum and a less curvy side. I can convince my self that it's less wide than the species on the left but as to less wavy? Wouldn't have thought so.

Luckily both these individuals are male so I was able to dissect to confirm their identity. Here they are side by side. Can you see a difference in pronotal shape?

I've confusingly swapped them in this image 😂

The aedagus of the right hand beetle (from the top photo) confirms it as O. puncticeps (see below it's not it's in fact rufibarbis). This turned up fairly regularly in the garden over the summer to light, and this year was the second most commonly recorded species.

The left hand beetle is a different species and its aedagus suggests it is O. puncticollis. This species appears to be much scarcer with very few recent records and those mainly in Kent. But once again I suspect the NBN isn't up to date and I imagine this species is a bit more widespread.

To my eye, at least the pronotal differences aren't that obvious. Especially when once factors in that these are encountered at night whilst light trapping. It reinforces the need to have comparative material and to dissect occasional males for confirmation. It would have been quite easy to miss this one.

EDIT: Having looked at this again and examining the inner sclerites of the aedeagus I can see that what I thought was puncticeps above is in fact rufibarbis which explains the problem I have had with the pronotal feature..... You live and learn.

EDIT: also the puncticollis might in fact be melletii so it's safe to say I've really messed this one up!

Apologies for the dreadful post title pun ! 😲