June 27, 2022

Distribution of Colour Forms in Volucella bombylans

In iNaturalist we are able to identify the named colour forms of Volucella bombylans.

I have tried to add these to as many V bomblylans observations as possible to see if anything interesting emerges. Because a great many of these observations are not yet Research Grade at the level of 'form' the data below are taken for searches including any ID of that form using the "ident_taxon_id =" URL.

The forms are:
f. bombylans - all black haired but for a red haired tail.
f. plumata - yellow haired around the sides and back of the scutum, and the base of the abdomen, with a white tail.
f. haemorrhoidalis - as plumata but with a red tail.
There are other rare forms that are unnamed.

Conventional wisdom is that f. plumata is the most common form with about 2/3 prevalence, f. bombylans constitutes almost all the rest. This is borne out in iNat data: of 1387 observations 883 are f. plumata (64%), 451 f. bombylans (33%) and just 53 f. haemorrhoidalis (4%).

However they do not appear to be evenly distributed. I haven't looked for any research on this, so it's perhaps likely things are already known, but I thought I'd put them out there anyway.

f. plumata



.
.
.
f. bombylans



.
.
.
f. haemorrhoidalis


According to the iNat data, it would seem that f bombylans is quite restricted to the area between the Pyrenees (or really central France) and the Urals.

There are no f. bombylans observations in Asia, compared to 21 f. plumata and 1 f. haemorroidalis (one would have expected about 7).

There is only one f. bomblyans observation southwest of a diagonal line across France from St Malo to St Tropez - that is on the West coast of France. None at all in Iberia - again one would have expected about 6 or 7 from 19 Iberian observations.

The other interesting thing about Iberia is the overrepresentation of f haemorrhoidalis. The Iberian observations break down as 12 f. plumata and 7 f. haemorrhoidalis, that is very similar to the 2:1 ratio normally observed between f. plumata and f. bomblyans, as if f. haemorrhoidalis somehow replaces f. bombylans in Iberia.

There are also no f. bombylans in Scotland, out of 25 observations.

The numbers are fairly small and I've done no statistical analysis of the significance of this, but it certainly seems quite interesting.

Posted on June 27, 2022 01:58 PM by matthewvosper matthewvosper | 7 comments | Leave a comment

June 13, 2022

Key to the Didea, Dideomima, Asiodidea and Megasyrphus of the World

These are the Syrphine genera with a dipped radial vein.

This has been a bit of a challenge, but quite a lot of fun. Use this key with caution of course, some of these species are very poorly known, others very variable. The genus Didea in particular I think needs revision, and who knows if geographic variation is hiding distinct species currently under the same name?

Anyway, I hope at least this disseminates some information about these rather nice species.

Posted on June 13, 2022 10:54 PM by matthewvosper matthewvosper | 3 comments | Leave a comment

May 31, 2022

Key to the Doros of the World

Doros!

I've not had much capacity the last few months, far too many curveballs to deal with. But I think this was a lunch-break well spent.

Posted on May 31, 2022 11:18 PM by matthewvosper matthewvosper | 2 comments | Leave a comment

February 04, 2022

Key to the Syrphus of North America

Here is an attempt at a key to the Genus Syrphus in North America. It is not always possible to identify to species from photos in this genus: many keys (including Vockeroth 1983, and van Veen (Europe)) start with features like the distribution of microtrichia on the wing membrane, and make heavy use of the colour of bristles on the knees or spicules under the middle basitarsus - so they are not exactly primed for photo ID! Hopefully the arrangement of this key makes the genus a little more accessible to photo ID, and crucially exposes some information on those rare species that create nagging doubts in the back of the mind. Many observations will still not be identifiable to species however.

One of the difficulties of identifying in this Genus is being sure of the genus in the first place! There are included some pointers to help with that. I have also included a slide of information on European Syrphus because there is significant overlap.

I have not illustrated the key itself (although there are images on some of the introductory slides), however the names of species at the points they key out are hyperlinked to iNat observations. Bear in mind that for many species, there are no iNat observations however: it is my hope that this key might help to dig them out! Many species are sexually dimorphic, so when comparing images, be sure to compare with the correct sex.

Please let me know of any errors of fact or clarity.

The species covered are:
attenuatus, currani, intricatus, knabi, opinator, rectus, ribesii, sexmaculatus, sonorensis, torvus, and vitripennis. There are also some comments on dimidiatus Fabricus 1781, dimidiatus Macquart 1834, doesburgi and monoculus.

Posted on February 04, 2022 12:12 AM by matthewvosper matthewvosper | 19 comments | Leave a comment

January 16, 2022

Key to the Syrphus of Europe

Syrphus is the type Genus of the Hoverflies. It is literally typical. But identification in this genus from photographs is hard, and often impossible. Information on the rarer species is also difficult to find. Here is my best effort at a key to this group that is optimised for photographs. Comments and corrections are especially welcome given that it's such a tricky group.

The species covered are admirandus, attenuatus, auberti, nitidifrons, ribesii, sexmaculatus, stackelbergi, torvus and vitripennis.

Posted on January 16, 2022 02:45 PM by matthewvosper matthewvosper | 0 comments | Leave a comment

January 06, 2022

December 31, 2021

Key to the Neotropical Eristalis

Here is a key to the Eristalis of the Neotropical region.

There is an excellent paper on 'The Eristalis Flower Flies of the Americas South of the United States' by F.C. Thompson. This covers all the species here, and includes a very useful key, as well as full descriptions of all the species. Almost all of my information comes from this paper. The Thompson key however includes some clauses not well tailored to photographic ID, and also includes a few Palpada species.

The advantages of doing another key are partly the opportunity to tailor it towards photographs, partly for accessibility, and partly as a consolidation of learning exercise for myself. The Neotropical Eristalis are mostly quite visually distinctive, and it is not necessary to resort to clauses such as 'aristae plumose or bare'.

I'm not quite covering the same area as the Thompson paper. The Mexican states bordering the USA can see species that are regarded as Nearctic: So Thompson includes E stipator, but E arbustorum is also recorded on iNat from those northern states, and there is the obvious potential for other species such as E hirta to cross the border. For that reason I'm not including the very North of Mexico: Species covered by this key are alleni, bellardii, bogotensis, circe, croceimaculata, gatesi, persa and tenax.

For the Nearctic Eristalis (including the northernmost states of Mexico) see the excellent key by @edanko and @zdanko.

The greatest difficulty in identifying Eristalis in this region is actually confusion with some of the many Palpada species. Bolder markings on the scutum, a bright scutellum, brighter markings generally, and thickened hind legs are all indications that you may in fact have a Palpada.

Posted on December 31, 2021 11:29 AM by matthewvosper matthewvosper | 9 comments | Leave a comment

December 24, 2021

Distinguishing Eristalis arbustorum and Eristalis abusiva

Eristalis abusiva is a rare Palearctic species of drone fly. It seems to increase in abundance towards the coast, but is found inland, and there are records from entirely landlocked countries. According to Barkalov (Checklist of the hover-flies (Diptera, Syrphidae) of Russia 2018) its range extends as far east as Japan.

As cool a species as it is, its main function in life seems to be to complicate the identification of the much more common E arbustorum, which is rather similar. Below I will give the standard means of distinguishing them and their pitfalls, but I will also try to supplement this with some thoughts of my own.

It is difficult to gauge the variability of a rare species. How many people have seen a large enough number? Here we see the value of a site like iNat, which might just have the biggest collection of abusiva specimens in the world! Male and female, and from a diversity of locations. (Still only 30 or so and counting). Some detailed pictures can also be found on Steven Falk's website

Thanks to @sbushes, @jeanpaulboerekamps, @waldgeist and @alexplayford for giving permission for me to use their pictures.

The characters covered are:
Published characters:
.1. Aristae
.2. Middle tibiae
.3. Male eyes
.4. Face stripe

Other Observations:
.5. Geography
.6. Face shape
.7. Hairiness
.8. Scutum dusting
.9. Female abdomen markings

Posted on December 24, 2021 11:17 AM by matthewvosper matthewvosper | 6 comments | Leave a comment

December 04, 2021

November 25, 2021

Identification of the major groups within Platycheirus (males)

The taxonomy of Platycheirus on iNat has recently had a bit of a sort out. The result is the use of the generic/subgeneric framework established by Mengual (2020), and within that the Species groups suggested by Vockeroth and developed by Young, Marshall and Skevington. These Groups are called 'Sections' in iNat, because that is the rank that is available. Within the albimanus Section are the complexes scutatus and clypeatus. So it looks like this:

Genus Pyrophaena (aka granditarsis Group) Holarctic
Genus Eocheilosia New Zealand
Genus Platycheirus Holarctic,Neotropical
Subgenus Tuberculanostoma (formerly a distinct Genus) Neotropical
Subgenus Pachysphyria (aka ambiguus Group) Holarctic
Subgenus Carposcalis (aka stegnus Group) New World
Subgenus Platycheirus Holarctic
Section manicatus Holarctic
Section peltatus Holarctic
Section chilosia Holarctic
Section pictipes Nearctic
Section albimanus Holarctic
Complex clypeatus Holarctic
Complex scutatus Holarctic
Not in a complex Holarctic

(European identifiers in particular should note that the definition of 'Section albimanus' used here still conflicts with the definition sometimes used in Europe i.e. those species with white maculae - as it did before. White spots species are spread through the groups. In the UK for example 4 species are considered albimanus Group in this 'white spots' sense: ambiguus is in Subgenus Pachysphyria, discimanus is in Section manicatus, but the other two (albiimanus + sticticus) are in Section albimanus. This is why the concept cannot be implemented in iNat - the taxa have different parents.)

The morphological delineation of the groups within the genus Platycheirus goes primarily with the modifications of the male foreleg. Here is an attempt at a key to the groups on that basis, largely based on Skevington:

1. a. At least some segments of the male foreleg modified in shape.
b. Male foreleg modified only by the presence of ornamental setae, if at all.
2
4
2. a. Male foretibia unmodified in shape (only tarsi expanded).
b. Male foretibia modified in shape.
Section manicatus
3
3. a. Male foretibia broadening gradually throughout its length.
b. Male foretibia broadened distinctly at the apex only.
Section albimanus
Section peltatus
4. a. Face extended well forwards into a prominent pointed snout, but hardly downwards, and with a prominent tubercle, Males dichoptic.
b. Face not extended forwards into a snout. Males holoptic.
Subgenus Tuberculanostoma
5
5. a. Male forefemur with long curled bristle at the apex.
b. Male forefemur without such a bristle.
Subgenus Pachysphyria
6
6. a. Long curled setae on male forebasitarsi.
b. Without long curled setae on male forebasitarsi.
Section chilosia
7
7. a. Male foretibia without ornamental setae (i.e. leg unmodified).
b. Male foretibia with long posterior setae.
Section pictipes
Subgenus Carposcalis
Posted on November 25, 2021 10:25 PM by matthewvosper matthewvosper | 0 comments | Leave a comment