A sub-millimetre beetle

Yesterday I wandered up through Uig Wood and had a look beneath various bits of bark for signs of life. I found masses of the globular springtail Dicyrtomina saundersi which, after all these years, I still can't say correctly. Barcode bum globbies, easy. 

Somehow, I spied the tiniest beetle I've ever self-found, slowly working its way along the underside of a piece of bark I'd just pulled away from a fallen log. Wow - it was proper small, probably about a millimetre or so! I wish I'd have taken a pic in situ, but I was so damned keen to get the thing into a pot that I didn't think of the camera until afterwards. Through my 10x handlens I could see abdominal segments projecting beyond the end of short, squared-off elytra. It had a wide, rounded pronotum and was a very pale orange colour. Looked like a tiny staph to me. 

Back indoors I gave it the ethyl acetate treatment, whereupon it became stuck to the glass at the very bottom of a tube. No amount of gentle (and not so gentle) tapping would release it. In the end I floated it out by pipetting water into the tube until it floated out onto tissue paper. Sorted! Right, now to card it....haha! 

It didn't go awfully well

Oops - there goes an elytron... 

I know what you're thinking - what a bloody amateur, even I could do better than that! Well yeah, you probably could too. But remember this is a very small beetle. In fact, just to show you how small -  

My finger pointing at the speck of dust that is my mystery beetle

It was at this point I figured I best ask for help. I emailed a pic to Mark Telfer, who quickly came back with the suggestion that it was a Ptinella and was quite likely to be Ptinella errabunda. Blimey! Ok, happily I have the precise book necessary for the job, so I can do this. Umm. 

Mark came back with the helpful suggestion of just checking the genitalia (on a beetle that measures less than a millimetre!!!) rather than trying the keys. SAY WHAT??? But it wasn't quite as crazy a suggestion as I initially thought. These beetles are so darn small that they are essentially transparent, all I had to do was whack it on a slide and use my compound microscope to compare the shape of the spermatheca to those in the book. Oh ok, that sounds easy.

I started off by floating it in a drop of water, which revealed why this family of beetles are colloquially known as the featherwing beetles. How lovely!

A bit crumpled, but definitely very feather-like. I'm glad I saw this! 

Alright, so now we know it's definitely a featherwing (not that I would ever doubt Mark's beetle IDs) so now for a peek at the spermatheca. Not sure quite where that lies, somewhere in the abdominal cavity obviously, presumably in the rear half? Rear third? Online searches did not help, neither did my books. All they show are what it looks like removed and floated in liquid, or as drawings. Ho hum, how hard can it be anyway? 

I managed to orientate the beetle onto its back and splayed the rear legs apart for a view of the abdominal underside....nope, I honestly don't know what it is I'm meant to be visualising here!

Backlit from below

There's an intriguing 'dark loop' beneath the left hind coxa. Could this be part of what I was looking for?

And it's no better when lit from above - WTF?!?!

I decided, for reasons best not talked about, that I needed to separate the abdomen from the thorax, insert a pin and slide it down the edge of the abdomen, thus allowing me to peel back the underparts and reveal the genitalia sitting there all nice and neat. This may sound like madness, but it's a trick that Roger Booth showed to Mark and apparently it works. You can read about it by clicking here. I first met Roger many years ago and Mark several years ago. They are both scrupulously thorough, careful, methodical chaps. I expect they'd make excellent brain surgeons. Not I. 

Abdomen safely detached - so far so good

I now had a bit of beetle roughly half a millimetre long to play around with. Just let that sink in. Half a bloody millimetre! And somewhere inside that half a millimetre was a distinctively shaped bit of a sex organ. Seemingly 'quite large' for the size of the beetle. Oh right, like maybe a TENTH of a millimetre then??? *sigh* I continued onwards....

Surprisingly good pic of the pronotal angles!

But what about the spermatheca, I hear you cry? Ok, hands up - I couldn't find it. Nope, nothing. I fumbled and bumbled and generally made a hash of it all. I had the abdomen down to the final 3 segments, but I was buggered if I could see anything resembling the pictures in the book. I bunged it into hot water to keep it moist. It filled with bubbles, which looked quite pretty, but didn't help. 

It seems the spermatheca must be situated higher into the abdominal cavity than I expected, hence would have been torn apart as I smashed my way through the segments with micropins narrower than the width of a human hair. Holy crap, these beetles are tiny!

So, in conclusion, I fluffed what ought to have been a perfectly do-able identification. But I'm not bitter. Look at it this way, I spotted a beetle that measures less than a millimetre in length, potted it and then dissected it. So I bodged it, yeah. But if you'd have told me a year ago that I'd be even attempting such a thing, I would have laughed and told you to piss off. But I am. 

I'm happy that I tried, even if (on this occasion) I failed.