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Melangyna species ID Please
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robinsects



Joined: 25 Aug 2008
Posts: 18

PostPosted: Mon Sep 01, 2008 1:24 am    Post subject: Melangyna species ID Please Reply with quote


Melangyna species (male) ?
P8140701 crop1

The Roughs
Yorkshire Bridge Common
14-8-2008

I am new to this identification lark so if anyone has any ideas on this one I would appreciate your comments.

Initially thought to be M. umbrellaterum based on close similarity to specimen on Elizabeth Grimes1 Flickr site Similar species mentioned in Stubbs - M. compositarum and M. labiatarum. There are but no photos available for these, but they are supposed to be citrus yellow rather than creamy white as is the case of M. umbellatarum (and in this specimen).
Other features which militate against M. umbellatarum are the thorax is dark brown rather than shiney black; there seems to be a dark dusting on the wings. This is not shown in the illustation Stubbs Plate 2 Fig 6a for M. umbellatarum. However there is mention of extensive wing cover with microtritia for compositarum /labiatum.

Photos onthe internet show abdominal hairs for compositarum /labiatum. But no evident hairs on this photo.

Curiously the small rounded spots (towards the front of tergite 2) fit well to M. lucifera but this is a species not reported in the UK only in France and Scandinavia. M. lasiophthalma has small spots but further back. Meligramma trianguliferum has small spots but triangular rather than rounded.

Impossible to tell whether hairs on the eyes even when the photo is blown up to high magnification.

Female assumed to be same species seen two days later in the same area - thought by timz501 to be possibly M. lasiophthalma.
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conopid



Joined: 03 Sep 2005
Posts: 342
Location: Shrewsbury, Shropshire

PostPosted: Mon Sep 01, 2008 11:43 am    Post subject: Reply with quote

Hi, I think this demonstrates why it's useful to take a specimen, rather than rely soley on photographs. In the absence of a specimen and looking at your photos I would say this is M umbellatarum as the other species really do not have such light creamy coloured spots. M umbellatarum seems to be about in reasonable numbers at present, so there is a good chance this is what you have seen.
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Roger K.A. Morris



Joined: 06 Nov 2005
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PostPosted: Mon Sep 01, 2008 10:24 pm    Post subject: Reply with quote

Hello

Melangyna cannot be done from photos. This certainly is not M. lasiophthalma - a spring species so really not a runner in August!

The most likely grouping is either M. labiatarum or M. compositarum but microscopic examination is needed to separate the males - females cannot be separated.

I'm afraid we don't accept records for those species that cannot be done by visual cues (about 80% of the fauna cannot be done reliably that way). We will accept records from established recorders who retain specimens; otherwise, I'm afraid we treat records with distinct caution because misidentifications from the picture-book approach are frequently wrong - too much relience on colours which are very variable. As a general rule, if the key does not allude to coplours then these are not the determining character - Alan spent a long time trying to find the simplest and most reliable characters - and still there are problems.

Regards

Roger
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robinsects



Joined: 25 Aug 2008
Posts: 18

PostPosted: Tue Sep 02, 2008 1:40 am    Post subject: Reply with quote

Hi Nigel/ Roger

Thanks for taking the trouble to look at the photos of the Melangyna specimens. I accept what you are saying about collecting voucher specimens. Though I think that the value of a good photograph in narrowing down the possibilites are greatly undervalued. The eye is good at picking up small differences that would be impossible to describe in a key. (The photo collection seems to me to be a great asset of this web site). If, from the photos, I could narrow it down to Melangyna compositum/labiatarum for instance that would be good enough for most of my recording purposes. I notice in Hoverflies of Sheffield and North Derbyshire, (Sorby 1987). Melangyna compositum/labiatarum is described as common (over 40 sites) whereas M. umbellatarum is described as uncommon but wide spread. So I suppose each would be equally likely. Do you think that the wing darkening evident in the photos could indicate the presence of microtrichia - and if so would this narrow down the possibilities?

Regards

Rob
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conopid



Joined: 03 Sep 2005
Posts: 342
Location: Shrewsbury, Shropshire

PostPosted: Tue Sep 02, 2008 7:25 am    Post subject: Reply with quote

Hi,
Personally, I find it is difficult to make out microtrichia on wings, even with good lighting and a microscope, so it is highly improbable that this feature can be detected from photographs of specimens in the field. I don't think this is what the photo is showing.

I always take specimens of Melangyna for confirmation of species. As Roger says, you can't really do the species with any confidence without a specimen.

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robinsects



Joined: 25 Aug 2008
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PostPosted: Tue Sep 09, 2008 12:29 am    Post subject: Reply with quote

OK I will have to try and net one next year
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Roger K.A. Morris



Joined: 06 Nov 2005
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PostPosted: Wed Sep 10, 2008 9:56 pm    Post subject: Reply with quote

Hello

I think the key point is that Alan Stubbs spent a very long time trying to find characters that would reliably ID specimens. The choice of options was a great challenge in many instances and so I'm afraid that the current trend towards photographic ID misses the point - taxonomy is a tricky thing and not something covered by photos in anything like the majority of instances. Believe me, if we could do ID by photos I would be keen - I ALWAYS feel an element of regret when taking specimens. BUT I feel even worse regret when a possibly valuable record has to be discarded because of a lack of specimens. The point is that the numbers killed are minimal, but the power of sound science can be profoundly important. We need the sound science to convince the doubters that climate change is actually happening and is affecting those plants and animals that I for one love deeply - it is my lifdelong desire to make sure that we defend plants and animals that are so terribly threatened.

Regards to all

Roger
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robinsects



Joined: 25 Aug 2008
Posts: 18

PostPosted: Thu Sep 11, 2008 12:13 am    Post subject: Reply with quote

Hi Roger

Accept what you are saying but find it perverse that the rarer a species is (and therefore the more unlikely its sighting), the more pressure there is to kill it to provide evidence of its (past) existence. I think there is a role for field photos of difficult-to-identify flies which are subsequently caught and positively identified.

Regards

Rob
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conopid



Joined: 03 Sep 2005
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Location: Shrewsbury, Shropshire

PostPosted: Thu Sep 11, 2008 9:26 am    Post subject: Reply with quote

Ah yes, but frequently it turns out that the supposedly rare species is not so rare at all, just under recorded because nobody bothered to look more carefully. Wink
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Roger K.A. Morris



Joined: 06 Nov 2005
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PostPosted: Thu Sep 11, 2008 10:30 pm    Post subject: Reply with quote

Hello Rob

From the recording scheme viewpoint I think the key issue is that today we have very skewed data. We have a compelling graph that compares numbers of records against difficulty of ID. That graph shows that in the period since 1975 the ratio has changed dramatically - the numbers of easily ID species has grown rapidly whilst the numbers of challenging species has dropped equally rapidly. This is something we touch on in the soon to be published review of statuses.

Crucial to this is that there are rare species that are easily ID e.g. Callicera aurata whose numbers have not dropped or have actually increased (& I think they genuinely have). Meanwhile there are comparatively common species such as Cheilosia vernalis whose numbers have not actually dropped, but which now appear to be much scarcer because they cannot be ID from photos or as field ID. Worse still are Pipiza or Sphaerophoria - if you relied on records alone then these would be mega rarities. Yet, the reality is they are quite widespread but only a few of us are willing to do them and kill specimens - so the picture of rarity is skewed by simplicity of ID. Translate that to insects in general then Large Blue is doing ok whilst Cheilosia bergenstammi is in trouble - utter rot but that is what recording is telling us - and some people believe it!

I'm very sympathetic to the issue of killing specimens but would point to the fact that we all jump in our cars and think nothing of imploding oncoming insects (many of which might be rare but are un identifiable from the pulp on the windscreen so are of no consequence). The danger (and it is real) is that people will think of biodiversity as the 20% that can be ID whilst the remaining 80% are ignored. Why worry if fungus gnats or Cheilosia latifrons don't exist any longer!

If we want to influence the politicians we need reliable and verifiable data - at the moment we are drifting into a situation where the data are crap and the doubters can argue with justification that we don't have a clue because no-one can say with certainty that the data are accurate - hence my agitation about making sure we get the ID right. Better one dead specimen and a strong body of evidence than no evidence and an extinct species.

Lets not fall out on this - we have already lost valuable recorders because of this argument - a terrible shame as the real losers are the insects we all care about.

Regards

Roger
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Mick Parker



Joined: 21 Sep 2005
Posts: 26
Location: Weymouth

PostPosted: Fri Sep 12, 2008 9:11 am    Post subject: Reply with quote

Hi Roger,
Yes!, I second that!, an excellent comment!
See you in the Autumn!
Cheers, Mick
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conopid



Joined: 03 Sep 2005
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Location: Shrewsbury, Shropshire

PostPosted: Fri Sep 12, 2008 12:38 pm    Post subject: Reply with quote

Roger and Mick et al,
We could do with a well prepared explanation of the need for collecting, which could be an expanded version of Roger's various posts on the subject. This could be made available via one of the navigation bar links perhaps entitled - Why Collect Specimens?

Then at least we can point correspondents to this, rather than repeatedly having to rehearse the argument. Also, the item could include maps to demonstrate some of the points being made. Hopefully, it might encourage some new blood to start collecting specimens, before it's too late and there is no-one left doing critical recording.

It could usefully include a mention of Roger's and Stuart's Volucella inflata catch and release work, plus the explanations outlined here and elsewhere on the site posts.

Perhaps something to chat about at the DF AGM?

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Tony White



Joined: 12 Mar 2006
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PostPosted: Sun Sep 14, 2008 10:48 am    Post subject: Reply with quote

The question of "taking" i.e. killing insects in order to identify them is a vexed one. I once requested permission to identify spiders in a SSSI. Permission was granted - on the understanding that none were taken or otherwise harmed. When I entered the reserve I found that dozens of nesting boxes were in situ, mostly occupied by Blue * (censored!) - birds which consume enormous numbers if spiders! Need I say more?
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robinsects



Joined: 25 Aug 2008
Posts: 18

PostPosted: Mon Sep 15, 2008 12:48 am    Post subject: Reply with quote

Hi Roger.

No danger of us falling out over this

Accept your point about requiring to capture species impossible to identify from photos. However, my feeling is that more species could be identified in the field from photos - the problem being that here is a dearth of photos of definitely identified specimens.

Sometimes a good photo enables at least the exclusion of some species possibilities. To take this case of Melangyna identification as an example this photo of M. umbellatarum on Chirpy UKs Flickr site seems to exclude this species as too black and white.



Also of course that it takes a lot of time and patience (and of course luck) to get the photo of the telling feature to clinch an ID.
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conopid



Joined: 03 Sep 2005
Posts: 342
Location: Shrewsbury, Shropshire

PostPosted: Mon Sep 15, 2008 9:12 am    Post subject: Reply with quote

Hi Rob,
You've hit on the big dilemna for any hoverfly field worker who wants to get good photos of species, but also wants to accurately record species present in any given locality. I like to photograph hovers and always have to decide whether or not to risk taking photos and seeing the specimen get away, or just catch it and be sure of identifying it. The latter choice is invariably the best, as so often one can't get a good enough, sharply focussed photo, and often even that is not good enough. If there appear to be a lot of specimens about, I nab one or two and then photograph any others I see. Best of all, is if I can photograph, then nab the specimen. That way you absolutely know what the beast in the photo is.

On balance the best way to record is definitely to take a specimen. It's a whole lot easier than trying to do IDs from photos. But it is always very nice to get good a photo, and very rewarding to do so, as your photos show. Razz

There's a few of my photos here: http://www.flickr.com/photos/insectman/sets/334671/

best wishes

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