RECORDS Syrphid (Hover) flies for ID

JRsbugs · #31 (**permalink**) 24-11-2009, 08:21 PM

Yes I agree with getting expert advice on the difficult ones

. I'm waiting for Roger to appear but I guess he's busy.

JRsbugs · #32 (**permalink**) 25-11-2009, 03:13 AM

After hours of researching Eristalis yet again

I have found some interesting factors which may make things easier!

The list includes 10 Eristalis sp. on Hoverfly.org

Hoverfly Recording Scheme - View Forum - The Species

I have eliminated two due to extreme rareness, locality and ID features. They are E. cryptarum with old records in the south-west, and E. similis wich is near non-existant and is similar to E. pertinax but I found that E. similis has black front tarsi, where E. pertinax has orange front tarsi.

I have identified with almost certainty 5 of the remainder 8. They are E. tenax, pertinax, arbustorum, intricaria and interrupta. I notice these last two are called interruptus and intricarius on the hoverfly.org site but on diptera.info they are the former which is possibly the updated version.

I have searched on diptera.info for other species and found out more, I also found on a google a French Key which translates a little strangely but gives a few extra pointers. These are based on the van Veen key which I once had but it's not now online and I lost my version in a crash.

Where it says 'This' it means 'present'.

Google Translate

Looking at my pics for the umpteenth time, I noticed some very slight differences in pics I have of E. arbustorum females as I had them named. On one above which shows the face of the female E. arbustorum you can see the feathery arista on the antenna. What was bothering me was the other pics which seemed to be the same beast but were taken 3 minutes before in the same location. I had the same problem with males, two different ones and it took a while to see they were different with one being E. interrupta (I believe!)

There is a key for some species we have on a Canadian site, it states E. arbustorum can have a thin black glossy median line on the face but the French key mentions this for E. abusiva.

http://www.canacoll.org/Diptera/Staf...s_Plate_4a.jpg

I once again searched on diptera.info and discovered that E. abusiva has a coloured sheen on the abdomen, which my first one has, the one showing the back view. I have other pics which don't show feathery arista, I think it would be visible to a degree as the arista are reasonably in focus. This fly looks to have a more yellow middle leg tibia also. I wasn't sure if the abdomen marks were the same due to the angle of the real E. arbustorum female but they were very similar.

Diptera.info - Discussion Forum: Eristalis but which one?

The other two, E. horticola and E. rupium can be identified by various features but I don't think I have had them yet, or I haven't had good enough pics in the past to know.

The other two pics of the female which I think could be Eristalis abusiva.

Tormentil · #33 (**permalink**) 25-11-2009, 09:30 AM

Quote:

Originally Posted by JRsbugs

..... I really should have a book,

British Hoverflies by Stubbs & Falk is very good.

JRsbugs · #34 (**permalink**) 25-11-2009, 09:17 PM

Quote:

Originally Posted by Tormentil

British Hoverflies by Stubbs & Falk is very good.

Thanks, yes I think I could do with that one but there's many other fly families I would like to invest in books for as well. The only one I can find at the moment is from PEMBERLEY NATURAL HISTORY BOOKS on Abe Books at £38.50 with P&P. Amazon don't have it in stock, only £30 inclusive there. One I would really love to have too is on Phorid flies from Pemberly Books at £125!

I have been getting a lot of disconnection problems so haven't been able to progress much lately. I thought it was the wind but could be busy times after school in particular up until 6pm, then it seems OK but not always. BT need to update the lines here I think!

Geoff F · #35 (**permalink**) 25-11-2009, 09:25 PM

Yes Stubbs is the book I use most. Not cheap but worth it if you have a special interest in hoverflies.

The French site in Janet's links also looks interesting. I have printed out as much as possible but have encountered a print size with the main key. I will certainly return there.

Stubbs uses interruptUS and intricariUS but his book is around 7 years old now so I'm not sure if the spelling has changed since then.

He says that for E. abusivus look for the mid tibia being entirely pale, or occasionally slightly dusky at the tip. And the arista is almost bare.

E. arbustorum has a completely pale dusted face in fresh specimens but this can be difficult to see in older well rubbed specimens.

E. interruptus has a small brown quadrate stigma on the wings. As previously mentioned. And a strong black facial stripe.

Look for a slight but distinctive wing shade on E. horticola and E. intricarius which could be mistaken for Merodon equestris.

A more defined wing cloud in E. rupium plus a pale hind meta tarsus

But it can all be difficult to spot from a photo.

Roger has entered up my confirmed sightings. I reckon that any expert in this field is always going to be busy.

ps. I've also been getting some unexpected disconnections and slowness at times, particularly on this site

JRsbugs · #36 (**permalink**) 26-11-2009, 11:16 PM

"Look for a slight but distinctive wing shade on E. horticola and E. intricarius which could be mistaken for Merodon equestris."

Also in Eristalis intricaria (sorry but I'm used to 'a' instead of 'us') the hind tibia has a pale section where Merodon equestris doesn't (if they are the only legs you can see). E. intricaria can also have some, or a lot of orange hairs on the thorax, I have had some in the past but don't have pics on this computer.

The wing shading can also be on E. pertinax so other features should be looked at for E. horticola, in particular male front leg femur with long yellow hairs, male and female hind femur "basal half yellow bicolor".

The Canadian key gives for E. rupium the stigma being more than 3.5x as long as it is wide (French site says 2x), and brown to black flagellum.

Now all we need to do is combine the two keys for the ones present on both

I have two pics of Eristalis intricaria taken on 22nd April 2009 and 25th August 2009. I have pics from last year taken in July.

JRsbugs · #37 (**permalink**) 26-11-2009, 11:28 PM

I tried to upload a few pics of Eristalis pertinax this afternoon, got 'page can't be displayed'. I didn't lose the connection but it stalled completely and that was after school was out.

Now I'm looking with a very critical eye at my many E. pertiinax pics and many don't look quite right although they can be very variable. As a result I have uploaded some females which show obvious orange front and mid tarsi. This I know can show some blackish shading in places but I'm not sure with some if it's a lot or a little, some also have a more rounded orange patch on the abdomen and shading on the wings as well as very long stigma (at least 3.5x), some are just wierd altogether. I have to knock my head against the brick wall once more with these.

Female Eristalis pertinax, two different. Note also the pale top section of the hind tibia which can help to separate it from E. tenax, that has an all dark hind leg.

JRsbugs · #38 (**permalink**) 28-11-2009, 05:32 PM

Eristalis pertinax males. I have pics from 15th April to 25th October 2009.

I have tried to post a selection of variations, some can be very hairy on the abdomen while others look smooth. The abdomen is usually very tapered and often curls under, but some have a smaller abdomen than others where you might be thinking you have something different.

Check the front and mid tarsi, usually bright orange but they can have a shade of black on them. The pale section at the top of the hind tibia will help separate it from E. tenax. Stripe down the face is not as broad as E. tenax. Notice also how much dark shading there can be on the wings.

You will see a fresh batch in the autumn which overwinter, in spring they may look much more faded and as you see one I had in summer was quite bald on the face.

JRsbugs · #39 (**permalink**) 28-11-2009, 06:04 PM

Eristalis tenax females.

I have pics from 14th June to 2nd November 2009. My first pic last year was 15th July and last 7th November so it seems to appear later than E. pertinax. You will notice very gravid (pregnant) females late in the season.

Look for the all dark hind leg, but the femur/tibia joint can be paler. The hind leg also has an inflated appearance. The front and middle tarsi are black. Stripe down the centre of the face more clear cut and broad but from a side view is not easily visible. Abdomen generally more rounded, it can be without the orange marks or they can extend as in the males.

JRsbugs · #40 (**permalink**) 28-11-2009, 07:36 PM

Eristalis tenax males.

My first pics this year were on 12th June, last on 4th November 2009.

Males much the same as females for ID, except the eyes are touching in the middle. The one on the Buddleia shows two rows of hairs on the eyes which can be useful for ID, it was presenting uncertainty due to the angle of the hind legs and an apparent orange hue at the base of the hind femur (most likey due to reflection on it's orange hairs) on one pic even though it looked a typical E. tenax. This might have suggested E. horticola. This particular male also has dark wing shading making things more difficult.