Pterostichus melanarius?

JRsbugs · #1 (**permalink**) 11-08-2010, 10:18 PM

Hi,

I've checked out what I can see, it seems to fit Pterostichus melanarius.

Around 18mm, taken on 9th August.

Is this correct?

Janet

haematocephalus · #2 (**permalink**) 11-08-2010, 11:20 PM

Or perhaps Pterostichus niger? The size and shape of the pronotum look closer to that I think.

JRsbugs · #3 (**permalink**) 12-08-2010, 12:24 AM

Take a look at the description of Pterostichus melanarius, main pointer here is:

Entirely black but for extremities of palpi and antennae

Now check the description for Pterostichus niger

jaguarondi · #4 (**permalink**) 12-08-2010, 07:38 AM

I don't think it's melanarius. It looks too elongate, particularly the head and the thorax is slightly cordiform. Also the sides of the elytra aren't straight. P. niger looks a better fit bit I'm not sure

JRsbugs · #5 (**permalink**) 12-08-2010, 02:09 PM

I can see that the shape could fit P. niger but does it have coloured extremities of palpi and antennae? It's not mentioned on the WCG.

On the other hand, for P. niger they mention "Head with 2 setae by the inner margin of the eye" which are visible on my beetle.

For P. melanarius it's mentioned "Antennae... pubescent from 4th segment" which mine are but it's not mentioned for P. niger.

It seems that not all details are given for each species.

Jason Green · #6 (**permalink**) 12-08-2010, 02:35 PM

Afternoon Janet,

Yes, sparsity of information is a bit of a draw-back on the 'Net! Have you seen the RES key for Carabidae yet? NHBS - RES Handbook Volume 4 Part 2: The Carabidae - Martin L Luff

Take care,

Jason

JRsbugs · #7 (**permalink**) 12-08-2010, 02:47 PM

It would be great Jason to have all these ID keys, but unless specialising in one field, or you have lots of money which doesn't have other uses, the cost can be prohibitive!

That's why I ask others with the knowledge.. but thanks anyway.

Jason Green · #8 (**permalink**) 12-08-2010, 02:52 PM

...pleasure.

jaguarondi · #9 (**permalink**) 12-08-2010, 04:17 PM

Both niger and melanarius should have two setae inside the eye. Some points of difference (acc to Lindroth) are
niger has 3 dorsal punctures on 3rd elytral interval, mel has 2
niger is sl bigger on average, and duller
the flattened area along the sides of the pronotum widens towards the base in niger not in melanarius

Hope that helps

kitscot · #10 (**permalink**) 12-08-2010, 04:29 PM

The diagnostic feature that seperates the two species in the dichotomous keys of Martin Luff's RES handbook is the 'claw bearing segments of tarsi' either with or without setae underneath. P. melanarius has setae while P. niger does not. Looking at the photographs, especially where the tarsal claw can be seen clearly, I would definitely fall on the side of this being P. niger.

Regards

Kit