Guerrilla beetling

Life took me into central Cambridge this morning for a couple of hours. The weather was cool and breezy but with a warm spring sun. I decided to spend my daily exercise having a walk along the bit of the River Cam that passes through the west of the city centre. There's flood meadow here which is still grazed and lots of old willows and poplars that always invite a closer look. 

Think these are 'Lombardy' poplars, a form of black poplar

There's also a fair amount of dead wood that has been left to do its thing, and it was to this that I gravitated after first realising that there wasn't much happening on the muddy bits around alongside the river. 

Poking about in these poplar logs, especially under the bark, revealed a new beetle which is common and widespread in the southern half of England but that I'd half forgotten existed and hence hadn't looked for it for a while.

The bark beetle, Bitoma crenata. It's only about 3mm in length but is still striking looking with quite a complex structure to its pronotum and elytra. Often found in small groups under the bark of a wide range of dead and dying tree species.

Whilst looking in a damp and well rotten willow log I also came across a new species of staph, and a big one at that.

With the shape of the head and the scimitar like mandibles I had pegged this as a species of Tasgius (rather than Ocypus), so was pleased to get home to find I was right.

The punctures on the pronotum were all of one size and the pronotum itself narrowed towards the rear. That plus the all black legs and (as it's a female) the shape of the last tergite, means this is T. melanarius. As opposed to T. winkleri.

Staph expert, Harald Schillhammer, in the follow up to a recent post on the Facebook Beetle group mentioned that he usually separates them by the punctation at the base of the pronotum close to the impunctate midline. In winkleri, the punctation there is as dense as on the disc, in melanarius it is less dense than on the disc with wider interstices.

I've not seen winkleri yet so will have to wait until I do to see if that holds true.