Sunday, 21 May 2017

A Cautionary Tale

I've recently been in contact with Murdo MacDonald, the records collator for the Highland Biological Recording Group (HBRG). You can check out their website by clicking here. He's been going through this blog checking for any glaring bloopers upon my part. Thankfully just six queries thus far (of over 600 species recorded) and nothing outright rejected, but this single line of text stood out like a death sentence

Microvelia reticulata -  Well off mapped range. Certain?

I had a bit of a panic at that, I'd been so sure the ID was good. Only one thing for it, trundle back and grab a few then double-check what they actually are. Problem is that the small backwater they inhabit is fast disappearing as the water level drops. Would there be any suitable habitat left at all? I had my dinner and set off to check (not much in life gets in the way of dinner...)

When the River Conon is running high there is an overspill channel that becomes filled with water. As the water level drops this channel is cut off resulting in a series of very shallow interconnected pools. These have been steadily reducing in size so that at the moment most of the channel is now completely dry. Would the Microvelia still be here or would they have died with the loss of the pools?

The overflow channel with just two tiny pools remaining
Happily I found several of the assumed Microvelia, scurrying across the surface at my approach. I scooped two into a small tube before investigating the only other body of standing water available

This pool is below the weir's overflow sluice. Note the river in the background
I was positively thrilled to see a whole horde of assumed Microvelia scatter for cover at my approach, at least 20 of them disappearing into the stony edges. Closer inspection showed them to be huddled onto pebbles, I guess the open meniscus offers no hiding places so they head straight to the shore. There are no aquatic plants in this pool, apart from tiny growths of freshwater algae on the rocks. Nothing emergent though. I potted up three of the tiny beasts, each being about 2 or 3mm in length, before heading back to check them at high magnification.

Back indoors I was a bit disappointed to discover that they were all nymphs, maybe the adults have died off after overwintering and breeding. The one I checked before was an adult, that was on 25th March. There's a piccie of it on this blogpage.

Here's what they look like through a microscope


This one, rather unfortunately, had pegged it in the tube. But at least I could get some half-decent pics of unusual angles


  

Anyway, regards Microvelia the feature to concentrate on are the tarsal segments of the hindleg. This from the key:

1st and 2nd segments of hind tarsi equal (Length apters 1.6-1.8mm, macro 1.8-2mm) - pygmaea
  
2nd segment of posterior tarsi twice as long as 1st  - couplet 2....  (between reticulata and buenoi)

The problem I had was seeing a second tarsal segment! Maybe they aren't developed yet in nymphs? Try as I might the tarsus seemed to be of just one segment. Unhelpful. Meh. There is, of course another obvious explanation but I wasn't considering this at the time...

There are three drawings in the key that show the general body shape of reticulata and buenoi, mine were a good match for reticulata being rather broader and more rounded in dorsal aspect.

I hate relying on Google Images for help, though they sometimes lead to good sites. Lots of websites later I still wasn't convinced. Mine certainly looked good but would Murdo accept them? Then I stumbled across a key for the wingless apters (and hopefully nymphs!) God bless Brian Eversham, he the man! Scroll down to the very bottom of this Key to Aquatic Bugs and read the bit about the shape of the segment behind the pronotum


That'll do for me! After all that fuss and frustration I checked the distribution of Microvelia pygmaea and M.buenoi in Scotland. And guess what - they don't occur! Microvelia reticulata is the only representative of the genus ever to have been recorded from Scotland. Sheesh.....anyway, all confirmed now. Hopefully.

I emailed Murdo with the 'good news' and he passed the details of this blog to the HBRG Hemipterist. Smug bugger that I am I could hardly wait for the verdict. This afternoon it arrived -

The pictures appear to me to show early instar nymphs of a Velia species photographed in a classic Velia habitat. 

There is a pale midline showing, the first antennal segment is comparatively long and strongly curved and the middle legs in particular are very long. There are no pale marks/white spots to the front of the pronotum (also present in nymphs). I can't see the metanotum clearly but the other characters ought to be enough. If it is a nymph that is already the adult size for Microvelia then it is likely that it will achieve a larger size as an adult.
So, I've strung the whole damn thing, fooling myself but thankfully not the expert! And, when you break it down as they have, it's pretty bloody obvious too. What do I need to take away from this (other than a red face and a big pointy hat with a 'D" on it?) Well firstly I need to run through keys from the beginning rather than from genus. The trouble with being a PSLer is that it means you know a bit about most things but aren't necessarily expert in any of them. And a bit of knowledge, as the saying goes, can be a dangerous thing. I also need to stop if something isn't fitting and start again. Keys aren't infallible but they are usually pretty good when it comes to stuff like tarsal segments.

So I got it wrong. I could beat myself up about it (in fact I already am - I can't help that) or I could say, hey - the process works. The recorder picked up on a suspect record and was proven right. It's an embarrassing episode for me, brand new recorder and I've chumped out already. But this is good, in a way. It means that I will be more stringent with future records, more rigorous with the keys and hopefully become a better recorder and naturalist for it. Yes I'd love to see 10,000 species in Britain. Yes I do try to find new species for my list. Yes I do intend to put Uig on the biological map. But not with duff records and misidentified species.

I took another look at the image of the "Microvelia" I caught in March. Curved first antennal segment and longer than expected middle legs. Pah. I need to slow it down a notch.

Right...on to the next query from Murdo *sigh*

In happier news I just added Greater Plantain to my 1000 Species in a 1KSQ tally, coming in at number 591 590. Growing at the base of the garden gate that I pass through several times a day every single day. 

4 comments:

  1. Nice one. Only fresh water in my patch is ponds in people's gardens, Jealous! Wonder if I could find a microvelia site down here somewhere

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    1. Not such a nice one any more Ali, they've just been re-identified as one of the Velia. I'll have to wait for them to grow up a bit, I think but the records will still go through - except under the correct name this time....

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  2. So last time you checked with the expert you had a new plant for Britain. Swings and roubndabouts ;)

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    1. Well yes, there is that, lol. Cheers me ol' mucka.

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