The Society for the study of flies (Diptera)

Gateside · 2012-01-13 20:06:08

Can anyone point me in the right direction with this fly, please.
Sunning itself today; quite a large fly, though smaller than (say) a bluebottle.
I can't recollect seeing a fly of this size with an orange abdomen.

Quite a few images, but no specimen - my wife scared it off before I could get anthing suitable to capture it.

I have loaded one good image of the rear view, and one lightened image of the front end (done to lighten the shadow under). I have other views, but no really clear ones of the side, so may not be able to use a key on it.

Any suggestions?

Nigel

Uploaded Images

oxycera · 2012-01-14 00:29:02

Looks like Phaonia subventa, or something very close.

Gateside · 2012-01-14 12:02:43

John, thanks for the guidance.
I am struggling with this, as usual. In order to see what general information was available on this, I see that Phaonia have a bend in the outwing which crudely helps to suggest this genus. It looks very much like one on a Notts web site (eakrings.com). But elsewhere I found a very detailed image, where the abdomen appeared to have a strong transverse buckle, whereas mine is very smooth and rounded, almost as if it has no segments.
I see there is some discussion previously on this forum for a P subventa, and the differences with P rufiventris But I don't know where they got the information on that.

I may be able to then, by comparing with some of my other photos, be able to make this ID more definite, either way.

Can you suggest where I look?
Thanks
Nigel

brianh · 2012-01-14 14:00:53

The part of the Phaonia key that is relevent to males is as follows:-

Thorax with 1 pair presutural acrostichal bristles. Scutellum entirely reddish-yellow or only darkened at extreme base. Median pair of presutural dark stripes seen from behind two-fifths width of the grey dusted stripe separating them = rufiventris.
OR
Thorax with 2-3 pairs presutural acrostichal bristles. Scutellum broadly darkened at base.
THEN EITHER
Arista + hairing hardly as wide as third antennal segment. Middle tibia with 2 posterior bristles. From behind median presutural dark stripes two-thirds width of stripe separating them = subventa.
OR
Arista wider than third antennal segment. Middle tibia with 3 posterior bristles. From behind width of presutural dark stripes one-third width of stripe separating them = bitincta.

There are other characters which are not visible from pictures, and the number of presutural acrostichals may vary (including on left and right).

Last edited by brianh (2012-01-14 14:04:42)

Gateside · 2012-01-14 16:43:32

Many thanks for that bit of the key, Brian.

I shall have a closer look, and maybe I can make out enough of that detail to make a decision

Nigel

oxycera · 2012-01-15 00:09:35

The presence of a well developed pd bristle on the last third of the hind tibia is a good pointer to Phaonia.
Getting to species level is really a matter of microscope work and good keys although of course experts in calypterate flies can deduce quite a lot from good photos.

Gateside · 2012-01-15 15:08:16

John, I am now trying Brian Harding's part key.

I am finding this a challenge, for several reasons: (a) my own inexperience, (b) the fact that the photos could better in parts, and maybe (c) this individual does not fit the key as well as some others.

I have loaded a few further images to explain. There is a head and antenna+arista, also a view of the bristles on the posteria of the mid-tibia, and also the p.a. bristles.

This is my train of thought in following the key.

Looks like there are 2 pairs of pa bristles across, in the presutural area, though some seem bigger than others. But it does look like there are 2 pairs that could be called bristles on either side of the mid line. (could be clearer, i agree).
Also scutellum does not comply with desc for rufiventris, nor does the width of the grey dusted area - the dark areas are quite wide, in fact comparable with width of pale strip. (viewed from the rear - the front views don't show much)

The scutellum is broadly darkened at the base.

The arista from the photo (esp on the fly's right antenna) shows no hairs, but they could be very fine and sparse.
The difficulty is in the mid tibia. Away from the bristles and hairs at the joint, I can see 2 large posterior bristles, and one half-sized one!

Am I making something out of a bristle that would otherwise not comply in size, or have I gone wrong, or have I been mislead on the previous points?

John, it seems to have a lot going for it being P. subventa after all.
But I am not happy about the half-bristle, and as I said, the other photos could be clearer.

Nigel

Uploaded Images

brianh · 2012-01-15 15:47:06

You middle picture does show three mid tibial posterior bristles which would point to P. bitincta.
However this does demonstrate the difficulty of identification from pictures when you are not able to take all the characters into consideration. I looked at my pinned examples to compare the scutellum of P. rufiventris and P. subventa - there is a clear difference in the darkening of the scutellum and yours is broadly darkened at the base. I only looked at one of several of my specimens of P. subventa under the microscope - it was missing a bristle on one of the mid tibia - it had been lost, but I could see its base (the other side had two). Under the microscope I could also look at the width of the hairing on the arista which is impossible to gauge from a picture, and also see the presutural acrostichals. However, the width of the thoracic stripes in mine do seem a little narrow. Only by looking under the microscope at all of the characters in the key is it possible for me to come to an identification that I am satisfied with for my specimens.

Last edited by brianh (2012-01-15 16:01:18)

Gateside · 2012-01-15 18:10:52

So the half a bristle does count , making it three in all. I did intend to get a specimen, as I said at the outset, but it flew off. So unless I see it again, I am tharted in getting a definite outcome.

Thanks for your help

Regards
Nigel

Gateside · 2012-01-15 19:51:30

I had to put this comment in as an extra!

I found a similar discussion on Diptera.info
http://www.diptera.info/forum/viewthrea … pid=107367

as to whether it was subventa or bitincta. It was unresolved. There was no rear view....
However, it seems that P subventa can in rare cases have 3 bristles on the mid tibia.
And in my example, the presutural vittae (the 2 median dark stripes, as they call it there) are very broad. So there is a consistency. Otherwise, my example really breaks the rule in the key.
Am I being unreasonable in suggesting that it has to be P subventa, or does that break a rule that there has to be total consistency in all visible factors?

Regards
Nigel

brianh · 2012-01-15 20:44:29

As I stated above it is useful to be able to take into account all of the described characters (some only observable by microscopic examination) and in difficult cases perhaps make a decision on the balance of the evidence.
However, I can add another factor to take into consideration - the distribution. In the Fonseca keys (1968) the distribution of P.bitincta is given as Southern England, and I understand that there may be no records north of Herefordshire. Unfortunately the NBN Gateway maps are not available at the moment to check for more recent records. Noting that you have Cumbria as your location then P. subventa which is more generally distributed would appear to be the safe choice of ID.

Last edited by brianh (2012-01-15 20:49:00)

Gateside · 2012-01-16 11:41:25

Brian, I checked the NBN maps at the start of the w/e, and it wasn't working then. Now, 7.30 am Monday, and still no joy. I do remember that subventa was present in Cumbria, but did not look at bitincta. But if what you say is correct about that one, it's hardly likely to turn up here.

That was a rather interesting struggle from the outset, and a steep learning curve for me. Next time, I do intend (if possible) to capture the specimen).

Thanks for your help
Regards
Nigel

PS I did look at the mid tibia on the other side, but due to the wing getting in the way, and then the shadow, all I can say is that there were 2 bristles, but I wouldn't swear that there were no more.

brianh · 2012-01-16 18:18:42

Maps on NBN Gateway now working. Very few records for P. bitincta. However, one in South Yorkshire in 1991. The NBN Gateway is often short of records for Muscidae, but it would certainly be Northerly and one of very few records if yours was P. bitincta.

The Society for the study of flies (Diptera)

#1 2012-01-13 20:06:08

help with fly which has orange abdomen & rear of scutellum

#2 2012-01-14 00:29:02

Re: help with fly which has orange abdomen & rear of scutellum

#3 2012-01-14 12:02:43

Re: help with fly which has orange abdomen & rear of scutellum

#4 2012-01-14 14:00:53

Re: help with fly which has orange abdomen & rear of scutellum

#5 2012-01-14 16:43:32

Re: help with fly which has orange abdomen & rear of scutellum

#6 2012-01-15 00:09:35

Re: help with fly which has orange abdomen & rear of scutellum

#7 2012-01-15 15:08:16

Re: help with fly which has orange abdomen & rear of scutellum

#8 2012-01-15 15:47:06

Re: help with fly which has orange abdomen & rear of scutellum

#9 2012-01-15 18:10:52

Re: help with fly which has orange abdomen & rear of scutellum

#10 2012-01-15 19:51:30

Re: help with fly which has orange abdomen & rear of scutellum

#11 2012-01-15 20:44:29

Re: help with fly which has orange abdomen & rear of scutellum

#12 2012-01-16 11:41:25

Re: help with fly which has orange abdomen & rear of scutellum

#13 2012-01-16 18:18:42

Re: help with fly which has orange abdomen & rear of scutellum

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