Never be without a pot (id-ing your dung beetle)

This morning I was crossing the forecourt of a petrol station when I spotted a huge fat (slightly squashed) beetle. It was too early to be embarrassed in front of normal people, so I scooped it up and popped it in the plastic pot in my bag. Never be embarrassed and never be without your plastic pot, that's my advice.

This would not be an ideal specimen for your collection (squashed with 5 legs only) but I thought it would show how I identified it.

You can tell (I hope) that it's a beetle, with its shiny wing covers (elytra) meeting neatly along its back. It has very distinctive antennae - they've got clubbed ends, which when you look down a microscope at them, prove to be made up of various layers.

Something like this, but mine has fewer plates. CC image by Kurt Kulac.

This tells you straight away that you're dealing with the superfamily Scarabaeoidea. This'll come out quickly in the key in 'Collins Insects' (first question - is it a ground beetle with 'rigid hind coxae' (the base of the legs)? no... second question - is it a weevil with elbowed antennae and snouty face? no... third question - does it have antennae with segments that form a 'lamellate club'? YES.

Then you can move to the Scarabaeoidea key. Again it's quite straightforward - are the antennae elbowed? (no - it's not in with the stag beetles). Are the elytra roughly sculptured (something like this)? (no, so it's not in the Trogidae). Are the jaws visible from above, and the antennae 11-segmented? It would seem yes, and that we are dealing with a member of the Geotrupidae - Dor or Dung Beetles. There are only eight of these in Britain, so I felt I ought to be able to get it to species level.

When I put the beetle under the microscope, it was amazing and revolting because complete panic was going on - mites were running about all over the corpse and tiny wormy creatures were waving like mad from every point (nematodes I imagine). Dung beetles are renowned for having mites and their only hope for survival is to catch a lift on another dung beetle. Tough luck this time you parasites. I feel a bit itchy having looked but I think that's psychosomatic, I don't think they're interested in me.

My next stop was the dung beetle key from the Royal Entomological Society. In their family key it mentions a strange feature that confirms it's in the Geotrupidae: the fact that the eyes are divided into two by a 'canthus'. But it seems the purpose of this is as yet unclear.

The remainder of the key is full of beetle-jargon, so I'll spare you and just show you my notes:

I found the RES key difficult to use right at the end so supplemented it with Mike Hackston's illustrated key, and I think I can reasonably confidently conclude I've got Geotrupes spiniger. 

A bit of internet searching also suggested Volume 2:2 of 'Beetle News' for some compare-and-contrast photos and descriptions to distinguish between G. spiniger and G. stercorarius - the jaws of spiniger have a lobey shape (which agrees with my own specimen).

Please do bring in your beetles and have a go at identifying them. If you get stuck perhaps we can crack it together - there's plenty of reliable beetle-related information on the internet which can help.