Saturday, May 12, 2007

A beetle in the family Carabidae

I am an amateur naturalist attempting to work out the identity of every living thing in my garden.

Beneath a large stone (at (1.7,1.7) -see here) I found the beetle shown in photo 1 (click to enlarge). Sadly, in moving the stone I must have inadvertently squashed him or her (can anyone tell me how to sex my beetle?) because shortly afterwards he (or she) dropped dead. I was, and am, genuinely sorry about this as I try hard never to harm the creatures appearing in this blog. It at least gave me an opportunity to examine my beetle in detail.

Photo 1 does not fully capture the colour of my beetle. In direct sunlight it was a more vivid metallic blue. Photo 2, a 40x magnified view of part of my beetle's back, shows up the colour more clearly.

Beetles (unlike earwigs! - see here) comprise the insect order Coleoptera. They are in part distinguished from other insects by the presence of :
i) hard or leathery elytra (wing cases) in place of forewings, and
ii) biting (rather than sucking) mouth parts.

The problem for any amateur attempting to identify a beetle's species is that there are just sooooo many of the little fellows. The oft-repeated quote is that of British geneticist, J. B. S. Haldane (1892-1964), who, when asked what he could infer about the mind of God replied that he must have "an inordinate fondness for beetles". Apparently, the book to own (I don't) as a serious beetle lover is the Die Kafer Mitteleuropus (The Beetles of Central Europe) which, as of 1981, ran to ten volumes. According to my (single volume) Beetles (K.W. Harde, Octopus Books 1984) some 370,000 species of beetle are known to science and perhaps five million (!) await discovery. In Europe there are 8,000 species and in the U.K. alone 4,000. What this all means in practice for the amateur is that it's best to cultivate a sense of satisfaction in being able to pin a beetle down to one of the 100-or-so (British) families. Any progress in identification beyond that is a bonus.

So, how does one set about identifying a beetle's family? As is so often the case in natural history, the key to successful identification is the careful recording of all the little features that one overlooks at first glance: do the elytra entirely cover the beetle's abdomen or stop half-way down; are the rear legs longer or shorter than the front; are the antennae 'plain' or 'feathery', how many segments do they have; do they taper to a point or end in a club-like swelling? And so on. In my case I was greatly assisted by the A Key to the Families of British Beetles (D.M. Unwin, no. 166 of Field Studies Council publications). This key is excellent for the amateur as it puts an illustration beside every piece of technical jargon - a wonderfully simply idea, but it is amazing how many books don't do this and how difficult they can be to use as a consequence.

Following Dr. Unwin's key I'm fairly confident my beetle is a member of the family Carabidae. A particular feature of this family is the presence of large stubby trocanters ("lumps" on the hind leg femurs) photo 3 (40x magnification) it's clear that my beetle has exactly this feature. Turning back to the book by Harde mentioned above, a picture therein of the particular Carabidae species Pterostichus cupreus seems a possible candidate, but without a more detailed description than is given, I don't claim a high level of confidence in this identification. If you're reading this and have a better suggestion do please leave a comment. If my beetle is P. cupreus apparently he/she is predatory (as are most members of Carabidae), feeding on aphids.

Finally, let us pause for a moment's silence in memory of my dear, departed beetle. Gone, but not...er...identified.

POSTSCRIPT

A huge thankyou goes to Oleg who, in his comment attached to this posting, identifies my beetle as the carabidae beetle Leistus rufomarginatus. This site has a good close-up photo. Thanks again Oleg.

3 comments:

Oleg said...

It is Carabid beetle Leistus rufomarginatus, predator of springtails (Collembola)

Henry Walloon said...

A huge thankyou Oleg!

From your long list of publications it's clear you're extremely expert on the coleoptera. It's a pleasure to have you stop by my blog.

Gaye from the Hunter said...

I've been catching up on some of your entries. You had a good result having someone who knows their beetles drop by.

I am amazed at the publications that are available to you in your part of the world.

I am also encouraged by your enthusiasm and researach endeavours - your enthusiasm is infectious.

A couple of pretty neat ground beetles showed up in my backyard last summer, but unfortunately they were not cooperative photographic subjects (I also will not harm my creatures just for the sake of study). It's been too cold for tiny critters, but no doubt, when the weather begins to warm up again, there will be bugs aplenty.

Cheers,
Gaye