Continuing a theme

I picked another tube of beetles from the fridge yesterday to work through as is my want when the sky darkens and the family don't need me. These particular ones were collected back in mid-June from cow dung in an old meadow in the next village to mine. So given my last post it was rather a coincidence that the first beetle I looked at was another species of Aleochara.

This was obviously a different species to the last one: darker, hairier and more 'chunky' in appearance. It started through the key rather well and with its mesosternum having a pretty much complete carina (sort of line/ridge down the middle) I was doing OK.

You then get to the more subjective part of the key ie are its legs stout or narrow. Also whether the hind tarsus including the claws is shorter than the tibia or not. No idea on the stoutness but I reckoned that the tarsi were just a bit shorter than the length of the tibia.

Next step is to look at how strongly punctured the elytra and abdomen are. Even looking at the crap photo above you can see that (especially where the light hits the end of the abdomen) the punctuation is strong. Having decided that you then have to decide whether the abdomen strongly narrows towards the end. I don't think so but the species that falls out here, intricata (with a narrowing abdomen), should also have reddish legs. My beetle's legs are very black indeed. 

That takes it to either being A. tristis or moesta. The key difference here is size with moesta being 3-5mm and tristis being 5-6mm. Staphs are notoriously difficult to measure consistently given the telescopic concertina nature of their abdomens, but this beetle is around 6mm. So should therefore be A. tristis.

I decided to dissect to make sure.

It looked like a pretty good match for tristis but I find these quite hard to judge. But as luck would have it as I was dissecting the capsule (bit above) from the sac, something akin to to a rolled up condom fell out and started to unravel. 

Turns out this large coiled flagellum is a diagnostic feature for this species and can be seen in the diagrams from the key.

Result! Was good for the confidence to have one of these go relatively smoothly but I'm sure there'll be something along soon to mess with my head.

Aleochara tristis is found mainly in the south-east of England on dung and carrion and is described by Welch as rare. But I imagine that as with a lot of these staphs the coverage is pretty poor and they are a bit more common than previously thought.